GENERAL INFORMATION ABOUT THE MERGER AND THE SPECIAL MEETING

         The following questions and answers are intended to address briefly some commonly asked questions regarding the proposed merger and the special meeting. These questions and answers may not address all questions that may be important to you. Please refer to the more detailed information contained elsewhere in this proxy statement/prospectus, its annexes and exhibits and the documents referred to or incorporated by reference in this proxy statement/prospectus. For instructions on obtaining the documents incorporated by reference, see "Where You Can Find More Information."

Why am I receiving this proxy statement/prospectus?

        Our Board has approved a reorganization of our corporate structure, which would include changing the jurisdiction of incorporation of our parent company from Delaware to England and relocating our principal executive offices and additional senior executive officers to the U.K. We would change the jurisdiction of incorporation of our parent company through a merger that will result in Aon UK becoming the parent company of the Aon group of companies and effectively will result in your owning shares in an English public limited company instead of shares in a Delaware corporation. The merger agreement requires stockholder approval, which is why we have called a special meeting of stockholders and sent you this proxy statement/prospectus.

Questions and Answers Relating to the Special Meeting Proposals

Who are the parties to the merger?

        The parties to the merger described in this proxy statement/prospectus are Aon Delaware and Market Mergeco Inc., or "Aon Mergeco," a newly formed Delaware corporation. Aon Mergeco is a wholly-owned subsidiary of Aon Holdings LLC, a newly formed Delaware limited liability company, or "Aon Intermediate." Aon Intermediate is a subsidiary of Aon Delaware.

What is the merger?

        Under the Agreement and Plan of Merger and Reorganization, or the "merger agreement," Aon Mergeco will merge into Aon Delaware (which we refer to as the "merger"), with Aon Delaware surviving the merger as a wholly-owned subsidiary of Aon Intermediate. Upon consummation of the merger, each issued and outstanding share of common stock of Aon Delaware will be converted into the right to receive one Class A Ordinary Share. Aon UK, together with its subsidiaries (including Aon Delaware), will own and continue to conduct our business in substantially the same manner as is currently being conducted by Aon Delaware and its subsidiaries.

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What are the major actions that have been performed or will be performed to effect the merger?

        Aon Delaware has taken or will take the actions listed below to effect the merger. Charts describing the ownership structure among Aon Delaware, Aon UK, Aon Intermediate and Aon Mergeco before and after the effective time of the merger are also set forth below.

Major Actions

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Aon Delaware formed Aon UK as its wholly-owned subsidiary.



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Aon Delaware deposited the Class A Ordinary Shares of Aon UK with EES Trustees International Limited and an affiliated nominee, or "EES". Aon Delaware and EES entered into a depositary agreement governing the deposit of the Class A Ordinary Shares with EES.



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Aon Delaware formed Aon Intermediate as its wholly-owned subsidiary.



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Aon Intermediate formed Aon Mergeco as its wholly-owned subsidiary.



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Conditional upon the effectiveness of the registration statement of which this proxy statement/prospectus is a part, (i) Aon Delaware will contribute all of its interests in the Class A Ordinary Shares to Aon Intermediate, and (ii) Aon Intermediate will contribute all of its interests in the Class A Ordinary Shares to Aon Mergeco.



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Conditional upon approval of the merger agreement by its stockholders, Aon Delaware will contribute all shares of Aon Intermediate to Aon UK.



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Aon Mergeco and Aon Delaware will merge, and Aon Mergeco will cause the Class A Ordinary Shares to be delivered to the Aon Delaware stockholders for exchange pursuant to the merger.

Structure Chart Prior to and after the Effective Time of the Merger

        The following diagram depicts our organizational structure before and after the merger. The diagram does not depict any legal entities owned by Aon Delaware other than those related to the merger nor any aspects of the reorganization that are anticipated to take place after the effective time of the merger.

What will be Aon's corporate presence in the U.K.?

        In conjunction with the reorganization, we plan to expand our already substantial presence in the U.K., which will include relocating our principal executive offices to the U.K. Many of our senior

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executive officers and key decision makers are already in the U.K., and we expect that more will move to the U.K. We also intend to hold more of our regularly scheduled board meetings in the U.K.

What will I receive in the merger?

        The merger agreement provides that each share of Aon Delaware issued and outstanding immediately prior to the effective time of the merger will be converted into the right to receive one Class A Ordinary Share of Aon UK.

Will the merger dilute my economic interest?

        No. Immediately after the effective time of the merger, your relative economic ownership in Aon UK will remain the same as your relative economic ownership of Aon Delaware immediately before the merger, subject to your receipt of cash in lieu of any fractional shares that you hold.

Why does Aon want to engage in the merger?

        The merger is part of a reorganization of Aon's corporate structure, which includes the relocation of the place of incorporation of our parent company and our principal executive offices to the U.K., and which we expect will enable us to expand our long-standing presence in the U.K. while concurrently investing in our business globally.

        We expect that the reorganization of our corporate structure, which we refer to as the "reorganization," will strengthen our long-term strategy by:

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Enhancing our focus on growth by positioning our resources more proximately to the geographic areas poised to experience the highest level of growth and which areas today derive a substantial portion of their risk coverage through the U.K. market;



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Enabling our Risk Solutions business to deliver superior value to our clients and differentiate us from our competition via key retail initiatives that are or will be substantially driven from the U.K., such as our Global Risk Insight Platform, or "GRIP", Programs & Facilities and Broking Excellence and key reinsurance initiatives that are or will be substantially driven from the U.K., such as facultative programs and further expanding our Aon Re Analytics capabilities;



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Allowing us to expand the penetration of our HR Solutions segment into Europe through London, the current base for much of our European consulting operations and growing our U.K. and Europe, the Middle East and Africa, or "EMEA", benefits administration and human resources business process outsourcing, or "HR BPO", business lines;



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Leveraging our development, retention and acquisition of professional talent and optimizing its geographic deployment around the world in each of our primary and developing markets;



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Optimizing our fiscal planning and capital allocation and reducing our global tax rate in a manner that provides us with increased financial flexibility to invest in our growth, Risk Solutions product innovation, HR Solutions expansion and talent development strategies while delivering increased shareholder value as follows:



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Providing greater global access, as a result of the U.K.'s tax rules regarding the repatriation of earnings, to expected increases in future cash flow as Aon delivers on its long-term operating margin targets while certain required uses of cash decrease over the next several years as restructuring costs decline and contributions to our material pension plans that are closed to new entrants and, where statutorily permitted, frozen from continued benefit accruals, are reduced as those plans become more fully funded;



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Enabling us to access approximately $300 million of excess capital held internationally on our balance sheet upon consummation of this reorganization;

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Increasing future cash flows through a significant reduction in our global tax rate over the long term due to changes in the geographic distribution of income, similar to the reduction achieved over the last five years, which would allow us to remain competitive with certain global competitors; and



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Delivering increased shareholder value as we effectively allocate capital through share repurchases and dividends.

        We also expect that the reorganization will result in operational and administrative efficiencies over the long term and enhance our ability to further expand in the Europe, Middle East & Africa and Asia Pacific geographic regions, which represented approximately 27 percent of our consolidated revenue for the year ended December 31, 2010 on a pro forma basis assuming the acquisition of Hewitt on January 1, 2010. As we continue to grow our business internationally, we believe that relocating our principal executive offices to the U.K. will provide increased strategic flexibility and operational benefits. We thus believe the merger will allow us to compete more effectively on a global scale. See "Proposal 1—Approval of the Adoption of the Merger Agreement—Background and Reasons for the Merger."

Will the merger affect current or future operations?

        Our principal executive offices will be moved to the U.K., which we expect will create more operational efficiencies. However, the merger is not expected to have a material impact on how we conduct day-to-day operations in the United States below the senior executive level. We expect, for example, to increase the size of our Chicago and other U.S.-based workforce as a result of the reorganization. While the new corporate structure would not change our future operational plans to grow our business or diminish our focus on our U.S. business, it may improve our ability to expand within our Europe, Middle East & Africa and Asia Pacific geographic regions. The location of future operations will depend on the needs of the business. Please see "Proposal 1—Approval of the Adoption of the Merger Agreement—Background and Reasons for the Merger."

What actions are expected to be taken following the merger?

        Following the consummation of the merger, Aon UK, as Aon Delaware's ultimate parent company, expects to examine various potential transactions that could bring about a further restructuring of Aon Delaware and certain of its subsidiaries. We refer to these activities and transactions in this proxy statement/prospectus as "subsequent actions." Refer to "Cautionary Statement Concerning Forward-Looking Statements" and "Risk Factors" below for a description of certain risks associated with the reorganization.

When do you expect to complete the merger?

        If the proposal to adopt the merger agreement is approved by our stockholders at the special meeting, we anticipate that the merger will become effective as soon as practicable following stockholder approval. We currently anticipate that the merger will be completed in the second quarter of 2012, although the merger may be abandoned by our Board at any time, including after stockholder approval. Please see "Cautionary Statement Concerning Forward-Looking Statements" and "Risk Factors."

Is the merger taxable to me?

        For U.S. federal income tax purposes, the conversion of each issued and outstanding share of the common stock of Aon Delaware into the right to receive a Class A Ordinary Share upon the consummation of the merger generally will be treated as an exchange of such share for the Class A Ordinary Share. Therefore, the U.S. federal income tax discussion contained herein refers to an "exchange" rather than a "conversion" in describing the U.S. federal income tax consequences of the merger.

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        Generally, for U.S. federal income tax purposes, a "U.S. holder," which is defined below in "Material Tax Considerations Relating to the Merger—U.S. Federal Income Tax Considerations—Material Tax Consequences to Stockholders," should recognize gain, if any, but not loss, on the receipt of Class A Ordinary Shares in exchange for Aon Delaware common stock in connection with the merger. A U.S. holder should generally recognize gain equal to the excess, if any, of the fair market value of the Class A Ordinary Shares received in the merger over the U.S. holder's adjusted tax basis in the shares of Aon Delaware common stock. Generally, this gain should be a capital gain. U.S. holders should not be permitted to recognize any loss realized on the exchange of their shares of Aon Delaware common stock in the merger. In determining the amount of gain recognized, each of the Aon Delaware shares exchanged should be treated as the subject of a separate exchange. Thus, if a U.S. holder exchanges some Aon Delaware shares on which gains are realized and other Aon Delaware shares on which losses are realized, the U.S. holder may not net the losses against the gains to determine the amount of gain recognized. In the case of a loss, the adjusted tax basis in each Class A Ordinary Share received by a U.S. holder should equal the adjusted tax basis of each share of Aon Delaware common stock exchanged therefor.

        Cash received by a U.S. holder in exchange for a fractional share of Aon Delaware common stock should be treated as having been received in redemption of such fractional share. Thus, gain or loss generally should be recognized by such U.S. holder in an amount equal to the difference between the amount of cash received and the U.S. holder's adjusted tax basis in such fractional share. A non-U.S. holder generally will not be subject to U.S. federal income tax on gain recognized, if any, on the exchange of Aon Delaware shares for Class A Ordinary Shares or on the receipt of cash in exchange for fractional shares of Aon Delaware common stock. Please see "Material Tax Considerations Relating to the Merger—U.S. Federal Income Tax Considerations—Material Tax Consequences to Stockholders."

        For U.K. tax purposes, stockholders of Aon Delaware who are residents of the U.S., and not residents of the U.K., will generally not be subject to U.K. taxation as a result of the merger. Generally, U.K. resident stockholders of Aon Delaware may realize a chargeable gain or an allowable loss for U.K. corporation tax or capital gains tax purposes (as the case may be) as a result of the merger, which will be treated as giving rise to a disposal of their stock in Aon Delaware. Generally, non-U.K. resident stockholders of Aon Delaware should not be subject to either U.K. corporation tax or capital gains tax as a result of the merger, unless they carry on a trade in the U.K. through a permanent establishment in the U.K. or through a branch or agency in the U.K. for the purposes of U.K. corporation tax or capital gains tax, respectively, and the stock is attributable to that permanent establishment, branch or agency. In general, you will be treated as acquiring the Class A Ordinary Shares received in the merger for consideration equal to the market value at the effective time of the merger of your shares of Aon Delaware common stock converted in the merger. Please see "Material Tax Considerations Relating to the Merger—U.K. Tax Considerations—Material Tax Consequences to Shareholders."

        For stockholders of Aon Delaware who are citizens or residents of, or otherwise subject to taxation in, a country other than the U.S. or the U.K., the tax treatment of the merger will depend on the applicable tax laws in such country.

        WE URGE YOU TO CONSULT YOUR OWN TAX ADVISOR PRIOR TO THE SPECIAL MEETING REGARDING THE PARTICULAR TAX CONSIDERATIONS OF THE MERGER FOR YOU.

Will Aon Delaware or Aon UK be taxed as a result of the merger?

        We believe that Aon Delaware and Aon UK should not incur any significant taxes in connection with consummation of the merger. Although changes in tax laws, treaties or regulations or the interpretation or enforcement of these tax laws, treaties or regulations could adversely affect the intended tax benefits of the merger to Aon UK and its subsidiaries or the tax treatment of the

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post-merger corporate structure of Aon UK, we do not believe that any of such changes would result in a material increase in taxes as compared to our current, pre-merger tax position.

Has the IRS or HMRC rendered a ruling on any aspects of the merger?

        No ruling has been requested from the U.S. Internal Revenue Service, or "IRS," in connection with the merger, and the IRS has adopted a policy of not issuing a ruling that a merger qualifies as non-taxable, unless there is a separate significant issue related to the merger. Furthermore, the IRS will not rule on whether the U.S. anti-inversion rules will apply to the merger. See "Material Tax Considerations Relating to the Merger—U.S. Federal Income Tax Considerations—The U.S. Anti-Inversion Rules."

        No ruling has been obtained from H.M. Revenue & Customs, or "HMRC," as to the U.K. corporation tax consequences of the merger. We have obtained a ruling from HMRC that, following the merger, the "temporary period exemption" from the U.K.'s controlled foreign company rules will apply such that, subject to certain conditions and limitations based on our facts and circumstances, Aon UK will not be subject to tax on the profits of any controlled company which is resident in a foreign jurisdiction under the CFC rules until 24 months after the end of the accounting period in which the merger occurs, subject to any changes of legislation. See "Material Tax Considerations Relating to the Merger—Material U.K. Tax Considerations—Material U.K. Tax Considerations Relating to and After the Merger—After the Merger—Controlled Foreign Companies". A ruling has also been obtained from HMRC regarding the U.K. stamp duty and stamp duty reserve tax ("SDRT") consequences of the merger. See "Material Tax Considerations Relating to the Merger—Material U.K. Tax Considerations—Material U.K. Tax Considerations Relating to and After the Merger—The Merger."

What types of information and reports will Aon UK make available following the merger?

        After the effective time of the merger, we will continue to prepare financial statements in accordance with U.S. Generally Accepted Accounting Principles, or "U.S. GAAP," and report in U.S. dollars, and will continue to file reports under the U.S. Securities Exchange Act of 1934, as amended, or the "Exchange Act," including reports on Forms 10-K, 10-Q and 8-K with the SEC, as we currently do. We also must comply with additional reporting requirements of English law.

        For so long as Aon UK has a class of securities listed on the New York Stock Exchange, or "NYSE," Aon UK will be subject to rules regarding proxy solicitations and tender offers and the corporate governance requirements of the NYSE, the Exchange Act and the U.S. Sarbanes-Oxley Act of 2002 including, for example, independence requirements for audit committee composition, annual certification requirements and auditor independence rules, unless certain circumstances change. Aon UK will be required to disclose any significant ways in which its corporate governance practices differ from those followed by U.S. domestic companies under the NYSE's listing standards. To the extent possible under English law, Aon UK's corporate governance practices are expected to be comparable to those of Aon Delaware. Please see "Proposal 1—Approval of the Adoption of the Merger Agreement—Stock Exchange Listing," "Comparison of Rights of Stockholders/Shareholders," and "Proposal 1—Approval of the Adoption of the Merger Agreement—Effect of the Reorganization on Potential Future Status as a Foreign Private Issuer."

What must I do to obtain ownership of Class A Ordinary Shares that I become entitled to receive as a result of the merger?

        If you hold Aon Delaware share certificates, you will be sent a letter of transmittal, which is to be used to surrender your Aon Delaware share certificates and to request that Class A Ordinary Shares be delivered to you. The letter of transmittal will contain instructions explaining the procedure for surrendering Aon Delaware share certificates and requesting Class A Ordinary Shares. YOU SHOULD NOT RETURN SHARE CERTIFICATES WITH THE ENCLOSED PROXY CARD.

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        If you hold shares as a record holder in direct registration form (under the Direct Registration System) without a share certificate you will not be required to take any action. Your Class A Ordinary Shares will be issued in accordance with the arrangements described below.

        Beneficial holders of shares held in "street name" through a bank, broker or other financial institution will not be required to take any action. Your ownership of Class A Ordinary Shares will be recorded in book entry form by your broker without the need for any additional action on your part.

        All shares delivered in connection with the merger will initially be delivered in a manner that will allow those shares to be transferred through the facilities of The Depository Trust Company, or "DTC". As a result, if you hold share certificates representing Aon Delaware shares or if you otherwise hold Aon Delaware shares as a record holder of uncertificated shares, your shares will initially be delivered to Computershare Trust Company, N.A., an affiliate, or another bank or trust company, as custodian for you, or the "Custodian", and held in its account at DTC. No former record holder of Aon Delaware whose Class A Ordinary Shares are delivered to the Custodian will be required to pay any fees to the Custodian for the initial 90 day period. Any such holder who wishes to transfer its shares from the custody of the Custodian to another bank or broker or to receive certificated Class A Ordinary Shares will not be charged any fees to do so by the Custodian or Aon UK. Following the effective time, former record holders of Aon Delaware shares will also be provided with terms and conditions governing their custody account. Shareholders who wish the Custodian to continue holding their Class A Ordinary Shares must provide the Custodian with "know your customer" information and other customary documentation and must agree to the terms and conditions. A failure to provide such information and agreement within 90 days following the effective time will result in such holders no longer holding their shares through the Custodian and instead holding shares as record holders of certificated shares of Aon UK. Certain non-U.S. shareholders will not be eligible to hold their shares through the Custodian after the initial 90 day period. Any such shareholders who do not inform the Custodian of another bank or broker to whom their shares should be transferred prior to the end of the initial 90 day period will be issued shares in certificated form. You should particularly note that subsequent transfers of Class A Ordinary shares may attract stamp duty and SDRT under U.K. law. For more information, see "Material Tax Considerations Relating to the Merger—U.K. Tax Considerations—Material U.K. Tax Considerations Relating to and After the Merger—Stamp Duty and SDRT." As a result, each former record holder is strongly encouraged to provide the documents and information requested by the Custodian in a timely manner, so the shares may continue to be held within the facilities of DTC.

        For more information, see "Proposal 1—Approval of the Adoption of the Merger Agreement—Ownership in Aon UK; Conversion of Shares; Delivery of Shares to Former Record Holders."

        It is expected that, prior to the effective time of the merger, Computershare Inc. and/or one of its affiliates will be appointed as the exchange agent for the merger, or the "exchange agent." Aon UK's current share registrar is Computershare Investor Services PLC, P.O. Box 82, The Pavilions, Bridgwater Road, Bristol BS13 8AE, England, which will continue to serve as the U.K. share registrar for its Class A Ordinary Shares after the effective time of the merger. It is also expected that prior to the effective time of the merger, Computershare Trust Company, N.A., 250 Royall Street, Canton, Massachusetts, 02021 will be appointed to act as Aon UK's U.S. transfer agent as required under the rules of the New York Stock Exchange.

If I hold share certificates representing Aon Delaware shares, what will be my rights in relation to Aon UK before I exchange my certificates for Class A Ordinary Shares?

        From and after the effective time of the merger and pursuant to the terms of the merger agreement, Class A Ordinary Shares for stockholders who hold share certificates in Aon Delaware will initially be held in "street name" through the Custodian and, for so long as such shares are held by the Custodian, will be required to exercise their rights through the Custodian. Until Aon Delaware stock certificates are surrendered for exchange, any dividends or other distributions declared by Aon UK

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after the effective time of the merger with respect to Class A Ordinary Shares delivered to former Aon Delaware stockholders, other than any Class A Ordinary Shares held by Aon Delaware or any other subsidiary of Aon UK, will accrue but will not be paid to the Custodian, as custodian for such holder, and holders of such shares will not have voting rights with respect to Aon UK. See "Proposal 1—Approval of the Adoption of the Merger Agreement—Ownership in Aon UK; Conversion of Shares; Delivery of Shares to Former Record Holders" and "Proposal 1—Approval of the Adoption of the Merger Agreement—Dividends and Distributions; Withholdings; Termination of Exchange Fund; No Liability." It is expected that Computershare Inc. and/or one or more of its affiliates will serve as exchange agent for the exchange of Aon Delaware certificates for Class A Ordinary Shares.

What happens to Aon Delaware stock options, restricted stock units and other equity-based awards at the effective time of the merger?

        As of the effective time of the merger, Aon UK will adopt and assume, and become the plan sponsor of, the Aon Stock Incentive Plan, the Amended and Restated Global Stock and Incentive Plan of Hewitt Associates, Inc., the Aon Corporation 2011 Incentive Plan, and each change-in-control agreement with a key employee and under the Aon Corporation Executive Special Severance Plan, each as may be amended from time to time. With respect to all other existing plan and arrangements, Aon Delaware will remain the plan sponsor. With respect to all equity incentive plans or arrangements, however, Class A Ordinary Shares, rights to Class A Ordinary Shares or benefits or amounts based on Class A Ordinary Shares will thereafter be granted or issued under each equity incentive plan instead of shares of Aon Delaware currently being granted or issued under such plans. Future awards would be subject to, and governed by, the terms of our equity incentive plans, as assumed by Aon UK if applicable, and any agreements entered into pursuant thereto. Please see "Proposal 1—Approval of the Adoption of the Merger Agreement—Stock Compensation and Benefit Plans and Programs" for more information, including a description of the tax withholding and regulatory consequences of the merger.

        At the effective time of the merger, all outstanding options to purchase shares of Aon Delaware common stock and all outstanding awards of restricted stock units and other equity-based awards granted to employees and directors by the Company under our equity incentive plans prior to the effective time of the merger will entitle the holder to purchase or receive, or receive benefits or amounts based on, as applicable, an equal number of Class A Ordinary Shares. All of such equity-based awards will generally be subject to the same terms and conditions as were applicable to such awards granted or issued by Aon Delaware immediately prior to the effective time of the merger.

Can I trade my Aon Delaware shares before the merger is completed?

        Yes. Aon Delaware common stock will continue trading on the NYSE through the last trading day prior to the date of completion of the merger.

After the merger, where can I trade my Class A Ordinary Shares?

        It is a condition to the completion of the merger that the Class A Ordinary Shares will be authorized for listing on the NYSE. We will submit an application to the NYSE and expect that, immediately following the effective time of the merger, the Class A Ordinary Shares will be listed on the NYSE under the symbol "AON," the same symbol under which your Aon Delaware common stock is currently listed. We have no current plans to list Aon UK's shares on any other securities exchange, including the London Stock Exchange.

Why am I being asked to approve a reduction of capital of Aon UK?

        Under English law, Aon UK will only be able to declare dividends, make distributions or repurchase shares out of "distributable reserves." Immediately after the merger, as a newly formed public limited company, Aon UK will not have any distributable reserves. In order to have sufficient distributable reserves to continue paying quarterly dividends and to repurchase shares on the

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anticipated schedule for the foreseeable future, Aon UK will seek to have an amount approximately equal to the sum of Aon Delaware's retained earnings and additional paid-in capital less Aon Delaware's outstanding indebtedness as of a date on or around the closing created as distributable reserves following a reduction of capital of Aon UK implemented through a customary and conventional one-time court proceeding. Please see "Risk Factors—English law will require that we meet certain additional financial requirements before we declare dividends and repurchase shares following the merger", "Proposal 1—Approval of the Adoption of the Merger Agreement—Dividends", and "Proposal 2—Implementation of a Reduction of Capital of Aon UK" for more information. In particular, the current shareholder of Aon UK (which is Aon Delaware) has passed a resolution to reduce the capital of Aon UK to allow the creation of distributable reserves following the merger. If the proposal to reduce Aon UK's capital is approved by Aon Delaware's stockholders as set forth in Proposal 2 and the merger is completed, we will seek to obtain the approval of the English Companies Court through a customary process, which is required for the creation of distributable reserves to be effective, as soon as practicable following the transaction. The approval of the English Companies Court is expected to be received within four weeks after the completion of the merger.

What will happen if stockholders do not approve the reduction of capital of Aon UK?

        The approval by Aon Delaware's stockholders of the reduction of capital of Aon UK through a customary court-approved process is not a condition to the completion of the merger. If stockholders do not approve the proposal to approve an implementation of a reduction of capital of Aon UK through a court-approved process, Aon UK would achieve the reduction in capital through other methods to allow it to declare dividends, make distributions or repurchase shares following the completion of the merger. These efforts may include certain customary intra-group reorganizations, which are established and often-used alternatives for the creation of distributable reserves in a U.K. public limited company, but which we believe to be less advantageous than the proposed court-approved reduction in capital.

Why am I being asked to cast an advisory, non-binding vote to approve compensation that certain named executive officers of Aon Delaware may receive in connection with the merger?

        The Securities and Exchange Commission has adopted rules that require public companies to seek an advisory, non-binding vote with respect to certain payments received by named executive officers in connection with mergers and other corporate transactions. Because certain compensation that has been awarded by Aon Delaware to certain of its named executive officers in connection with the merger and their relocation to the U.K., or the "relocation compensation", may be deemed to be subject to these rules, we are holding an advisory vote regarding the relocation compensation.

Under what arrangements would relocation compensation be payable?

        Such compensation would be payable under international assignment letters entered into by Aon Delaware and the relocating executive officers. For more information, see "Proposal 1—Approval of the Adoption of the Merger Agreement—Interests of Directors and Executive Officers in the Merger".

What will happen if stockholders do not approve the relocation compensation at the special meeting?

        Approval of the relocation compensation that may be payable to certain of Aon Delaware's named executive officers in connection with the merger and their relocation to the U.K. is not a condition to completion of the merger. The vote with respect to such compensation is an advisory vote and will not be binding on Aon Delaware. Therefore, if the merger agreement is adopted by the stockholders and the merger is completed, the relocation compensation payable to certain of Aon Delaware's named executive officers will still be paid regardless of the outcome of this advisory vote.

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What is the voting requirement to approve the proposal to adopt the merger agreement? What is the voting requirement to approve the other proposals?

        For the merger to be able to proceed, at least two-thirds of the outstanding shares of common stock of Aon Delaware entitled to vote at the special meeting must be voted in the affirmative for the adoption of the merger agreement, as set forth in Proposal 1. Each of the other proposals will be approved if it receives the affirmative vote of the holders of a majority of the shares of common stock of Aon Delaware present in person or represented by proxy at the special meeting and entitled to vote thereon, whether or not a quorum is present.

What is the Board's voting recommendation?

        Our Board recommends that you vote your shares as follows:

         Proposal 1—FOR the adoption of the merger agreement;

         Proposal 2—FOR the approval of the implementation of a reduction of capital of Aon UK through a customary court-approved process so that it will have sufficient distributable reserves under U.K. law;

         Proposal 3—FOR the approval of the relocation compensation; and

         Proposal 4—FOR the approval of any adjournments of the special meeting to a later date to solicit additional proxies if there are insufficient votes at the time of the special meeting to approve the adoption of the merger agreement.

Questions and Answers Relating to the Special Meeting

When and where is the special meeting?

        Our special meeting will take place on March 16, 2012, at 1:00 p.m., local time, at the offices of Aon Corporation, located at the Aon Center, 200 East Randolph Street, Chicago, Illinois.

Who is entitled to notice of and to vote at the special meeting?

        Only stockholders of record on the record date ( i.e. , February 6, 2012) are entitled to notice of, and to vote at, the special meeting. As of the record date, our directors and executive officers and their affiliates beneficially owned, in the aggregate, approximately 1,049,455 of such shares, representing beneficial ownership of less than 0.32 percent of the outstanding shares of Aon Delaware common stock as of that date, and these shares are included in the number of shares entitled to vote at the special meeting.

Who may attend the meeting?

        Only Aon Delaware stockholders on the record date may attend the special meeting. If you are a stockholder of record, you will need to present the proxy card that you received, together with a form of personal photo identification, in order to be admitted into the meeting. If you hold your shares in "street name," you will need to provide proof of ownership, such as a recent account statement or letter from your bank, broker or other nominee, along with a form of personal photo identification. No cameras, recording equipment, electronic devices, large bags, briefcases or packages will be permitted into the meeting or adjacent areas. All other items may be subject to search.

What is this proxy statement/prospectus?

        This document serves as the proxy statement of Aon Delaware in connection with the solicitation of proxies to obtain votes on a proposal to adopt the merger agreement and the other proposals described herein. This document is also a prospectus of Aon UK for purposes of the U.S. Securities Act of 1933, as amended, or the "Securities Act," in connection with the issuance of Class A Ordinary

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Shares. For the avoidance of doubt, however, this proxy statement/prospectus is not intended to be and is not a prospectus or circular for purposes of the U.K. FSA's Prospectus Rules and Listing Rules.

We encourage you to read this proxy statement/prospectus carefully.

What is being delivered with the proxy statement/prospectus?

        These proxy materials include:

•

The notice of special meeting and proxy statement/prospectus for the special meeting; and



•

The accompanying proxy card (or voting instruction card from your broker or other intermediary) to register your vote on the proposal to adopt the merger agreement and the other proposals described herein.

Why am I receiving paper copies of these proxy materials when previously I received only a "Notice of Internet Availability of Proxy Materials" for the Company's annual stockholders' meeting?

        Under SEC rules, we are required to distribute paper copies of these proxy materials because of the subject matter of the business to be conducted at the special meeting.

Who is soliciting my proxy?

        Proxies are being solicited by the Board of Aon Delaware.

Who is paying for the cost of this proxy solicitation?

        We are paying the costs of soliciting proxies. Upon request, we will reimburse brokers, banks, trusts and other nominees for reasonable expenses incurred by them in forwarding the proxy materials to beneficial owners of shares of our common stock.

        In addition to soliciting proxies by mail and over the Internet, our Board, our officers and employees, or our transfer agent, may solicit proxies on our behalf, personally or by telephone, and we have engaged a proxy solicitor to solicit proxies on our behalf by telephone and by other means. We expect the cost of our private proxy solicitor to be approximately $20,000. We will also solicit proxies by e-mail from stockholders who are employees or who previously requested proxy materials be sent electronically. Arrangements also may be made with brokerage houses and other custodians, nominees and fiduciaries for the forwarding of solicitation materials to the beneficial owners of Aon Delaware shares held by those persons, and Aon Delaware will reimburse such persons for reasonable expenses incurred by them in connection with the forwarding of solicitation materials.

        Stockholders that vote through the Internet are advised that there may be costs associated with electronic access, such as usage charges from Internet access providers and telephone companies that will be borne by the stockholder in order for the stockholder to connect to or access the Internet site.

Whom should I contact with questions?

        We have retained Georgeson as proxy solicitor in connection with the special meeting. Our stockholders may contact our proxy soliciting agent at:

199 Water Street, 26 ^th  Floor
New York, NY 10038

Banks and Brokers may call (212) 440-9800
All others may call toll-free at (866) 647-8869

Where are Aon Delaware's principal executive offices located and what is the main telephone number?

        Aon Delaware's principal executive offices are located at 200 East Randolph Street, Chicago, Illinois 60601 and the main telephone number is (312) 381-1000.

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What is the quorum requirement for the special meeting?

        For purposes of the special meeting, the holders of at least a majority of the shares of our common stock issued and outstanding and entitled to vote at the special meeting, present in person or represented by proxy, will constitute a quorum. For purposes of determining whether there is a quorum, abstentions and broker "non-votes," described below under "What happens if I do not give specific voting instructions? How are broker non-votes treated?" and "How are abstentions treated?", are treated as shares that are present.

What is the difference between holding shares as a stockholder of record and as a beneficial owner of shares held in street name?

        Stockholders of Record.     If your shares are registered directly in your name with our transfer agent, you are a "stockholder of record" with respect to those shares, and this proxy statement/prospectus was sent directly to you by us. As a record holder, you vote your shares directly by following the instructions set forth in the enclosed proxy card.

        Beneficial Owners of Shares Held in Street Name.     If your shares are held in the name of a broker, bank, trust or other nominee as a custodian or in the general account of the broker or other organization, you are a "street name" holder. Consequently, this proxy statement/prospectus was forwarded to you by that organization. The organization holding your account is considered the stockholder of record for purposes of voting at the special meeting. As a beneficial owner, you have the right to direct that organization on how to vote the shares held in your account by executing a voting instruction card. You should receive information regarding voting instructions directly from that organization.

If I am a stockholder of Aon Delaware, how do I vote?

        Stockholders of Record.     If you are a "stockholder of record," you have several choices. You can vote your shares by following the specific instructions provided on the proxy card:

•

via the Internet at www.envisionreports.com/Aon;



•

over the telephone by calling (800) 562-VOTE (8683); or



•

by mailing in the proxy card.

        Beneficial Owners of Shares Held in Street Name.     If you hold your shares in "street name," your broker, bank, trust or other nominee will arrange to provide materials and instructions for voting your shares.

        Beneficial Owners of Shares Held in the Aon Savings Plan.     If you are a current or former Aon Delaware employee who holds shares in the Aon Savings Plan, you will receive voting instructions from the trustee of the plan for shares allocated to your account. If you fail to give voting instructions to the trustee, your shares will be voted by the trustee in the same proportion as shares held by the trustee for which voting instructions were received. To allow sufficient time for voting by the trustee and administrator of the Aon Savings Plan, your voting instructions for shares held in the plan must be received by 5:00 p.m. Eastern Daylight Time on March 13, 2012.

What happens if I do not give specific voting instructions? How are broker non-votes treated?

        Stockholders of Record.     All properly executed proxy cards received by the Board from stockholders of record that do not specify how stock should be voted will be voted "FOR" the proposal to adopt the merger agreement and each of the other proposals. With respect to any other matter that may properly be brought before the special meeting, the shares shall be voted in accordance with the judgment of the person or persons named on the proxy card.

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        Beneficial Owners of Shares Held in Street Name.     If you are a beneficial owner of shares held in street name and do not provide the organization that holds your shares with specific voting instructions, under the rules of various national and regional securities exchanges, the organization that holds your shares may generally vote on "routine" matters but cannot vote on "non-routine" matters. If the organization that holds your shares does not receive instructions from you on how to vote your shares on a non-routine matter or otherwise elects not to vote your shares in the absence of your direction on a routine matter, the organization that holds your shares will inform our Inspector of Election that it does not have the authority (or otherwise declines) to vote on such matter with respect to your shares. This is generally referred to as a "broker non-vote."

        A vote on the proposal to adopt the merger agreement is regarded as a non-routine matter and failure to direct your broker on how to vote on such a proposal has the same effect as a vote AGAINST it. A broker non-vote with respect to any of the other proposals will have no effect. We encourage you to provide voting instructions to the organization that holds your shares by carefully following the instructions provided in the proxy card or voting instruction card.

Can I vote my shares in person at the special meeting?

        Stockholders of Record.     If you are a "stockholder of record," you may vote your shares in person at the special meeting.

        Beneficial Owners of Shares Held in Street Name.     If you hold your shares in "street name," you must obtain a proxy from your broker, bank, trust or other nominee giving you the right to vote the shares at the special meeting.

How are abstentions treated?

        In determining the number of votes cast for a proposal, shares abstaining from voting or not voted on a matter will be counted for quorum purposes. However, shares abstaining from voting or not voted with respect to any of the proposals will have the same effect as a vote AGAINST it.

May I change my vote after I have voted?

        You may revoke your proxy or otherwise change your vote by doing one of the following:

•

by sending a written notice of revocation to our Secretary that must be received prior to the special meeting, stating that you revoke your proxy;



•

by signing and submitting a later-dated proxy card that must be received prior to the special meeting in accordance with the instructions included in the proxy card; or



•

by attending the special meeting and voting your shares in person.

        If you voted electronically or by phone, you can also change your vote before the special meeting. Follow the same voting process and your original vote will be superseded.

        If you are a beneficial owner of our shares and a broker or other nominee holds your shares, you can revoke your proxy or otherwise change your vote by following the instructions provided by your broker or other nominee.

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PROPOSAL 1—APPROVAL OF THE ADOPTION OF THE MERGER AGREEMENT

         The following includes a brief summary of the material provisions of the merger agreement, a copy of which is attached as Annex A and incorporated by reference into this proxy statement/prospectus. We encourage you to read the merger agreement in its entirety for a more complete description of the merger. In the event of any discrepancy between the terms of the merger agreement and the following summary, the merger agreement will control.

The Merger Agreement

Introduction

        The merger agreement you are being asked to adopt at the special meeting provides for a merger that would result in your shares of Aon Delaware common stock being converted into the right to receive Class A Ordinary Shares of Aon UK which will be, at the effective time of the merger, a public limited company incorporated under English law. Aon UK, together with its subsidiaries, will thereafter own and continue to conduct our business in substantially the same manner as is currently being conducted by Aon Delaware and its subsidiaries. Immediately following the merger, you will have the right to receive Class A Ordinary Shares of Aon UK, which will be managed by the same board of directors and executive officers that manage Aon Delaware immediately prior to the merger. Additionally, the consolidated assets and business of Aon UK immediately after the merger will be the same as those of Aon Delaware immediately prior to the merger.

        Under the merger agreement, Aon Mergeco, a wholly-owned subsidiary of Aon Intermediate (which itself is currently a wholly-owned subsidiary of Aon Delaware) will merge with and into Aon Delaware, with Aon Delaware surviving the merger as a wholly-owned subsidiary of Aon Intermediate. If the merger agreement is adopted by the stockholders, we anticipate that the merger will become effective shortly after such approval, subject to the making or receipt of applicable regulatory filings, registrations, consents and approvals. We currently anticipate that the merger will become effective in the second quarter of 2012.

The Parties to the Merger

        Aon Delaware provides risk management services, insurance and reinsurance brokerage, and human resource consulting and outsourcing, delivering distinctive client value via innovative and effective risk management and workforce productivity solutions. Aon Delaware delivers its technical expertise locally through colleagues worldwide.

        We serve clients through the following businesses:

•

Risk Solutions acts as an advisor and insurance and reinsurance broker, helping clients manage their risks via consultation, as well as negotiation and placement of insurance risk with insurance carriers through our global distribution network.



•

HR Solutions partners with organizations to solve their most complex benefits, talent and related financial challenges, and improve business performance by designing, implementing, communicating and administering a wide range of human capital, retirement, investment management, health care, compensation and talent management strategies.

        Our clients include corporations and businesses, insurance companies, professional organizations, independent agents and brokers, governments, and other entities. We also serve individuals through personal lines, affinity groups, and certain specialty operations.

        Aon Mergeco is a newly formed Delaware corporation and currently is a wholly-owned subsidiary of Aon Intermediate, which is a newly formed Delaware limited liability company and currently is a wholly-owned subsidiary of Aon Delaware. Neither Aon Intermediate nor Aon Mergeco has a

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significant amount of assets or liabilities and neither has engaged in any business since its formation other than activities associated with its anticipated participation in the merger.

        The principal executive offices of Aon Delaware, Aon Intermediate and Aon Mergeco in the U.S. are currently located at 200 East Randolph Street, Chicago, Illinois 60601, U.S.A., and the telephone number of each company is (312) 381-1000.

        The principal executive offices of Aon UK are currently located at 8 Devonshire Square, London EC2M 4PL, England, and its telephone number is +44 20 7623 5500.

Background and Reasons for the Merger

Background

Current U.K. Operations

        Aon has had a long-standing history and presence in the U.K. Aon was created in 1982 when the Ryan Insurance Group merged with Combined International Corporation. In March of 1987, the shareholders voted to change Combined International Corporation's name to Aon. Aon expanded rapidly during the 1980s and 1990s through several strategic acquisitions that enabled the company to reposition itself as a premier global insurance and reinsurance broker with close ties to the Lloyd's market. Aon acquired numerous brokers during this period with a strong Lloyd's heritage, one of the oldest having been a Lloyd's broker since 1823. Among the UK brokers acquired by Aon during this period were: Agricultural Risk Management, Asset Security Managers, Bain Hogg, Bishopsgate, Jenner Fenton Slade, Live Wire Group, Minet, Nicholson, Chamberlain & Colls, NYA Brand, Open & Direct Group Limited (Footmann James), Reed Stenhouse, Sinser Holdings AB, Supercover, Surety & Guarantee Consultants Ltd, Water for Fish, and Z Yen Limited. In addition, Aon acquired several global brokers that had a substantial UK presence, including Alexander & Alexander Services Inc., Frank B. Hall, Gallagher Re and Benfield. Over its recent history, Aon has also acquired several consulting firms with substantial UK operations, including, Surety & Guarantee Consultants Ltd., Water for Fish, Z Yen Limited, Live Wire Group, Agricultural Risk Management and NYA Brand.

        London continues to be a key geographic center of our global business. Aon has a substantial retail insurance brokerage business that places insurance on behalf of its UK-based clients. In addition, our Risk Solutions business currently places coverage in London for a large number of risks on behalf of non-UK-based clients requiring the expertise and breadth of the insurance offerings available in the mature London market. While certain basic insurance policies can be placed locally in many jurisdictions around the world, we will typically place complex or large policies in London. For example, a client in Houston may be able to easily secure basic property insurance on a small office building from a local carrier. However, that same client would be unable to insure its portfolio of oil platforms in the Gulf of Mexico, as the expertise and financial backing to cover that risk exists almost entirely in London. In its role as that client's broker, the local Aon affiliate will work with Aon brokers stationed in the Lloyd's of London market to arrange for the policy to be placed. In addition, the Lloyd's market operates through syndicates of global carriers, which share the relevant risks related to the placement. This allows Aon clients to access a diverse carrier listing which bear global risks, and are less impacted by local factors.

        Lloyd's of London has a long tradition of being the most exclusive and preeminent insurance and reinsurance market in the world, having developed over the last three hundred years through the interactions between brokers and underwriters. Lloyd's remains a relationship-driven operation that requires face-to-face interaction between brokers and underwriters. Business is conducted in the underwriting room at the Lloyd's Building, where brokers have immediate access to underwriters to negotiate and agree on pricing for the policies placed on behalf of clients. As most of the risks placed through Lloyd's are often large, complex, and highly individualized and large-scale, in-person

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negotiations are critical to successfully placing insurance and reinsurance policies. Maintaining a close connection with the insurance underwriters that operate at the Lloyd's market continues to be an important driver of our business.

        In addition, we have a number of specialty groups that make a substantial proportion of their placements in London. These include the Energy, Power, Mining, Marine, Aviation, Construction, Crisis Management, and Professional Services Groups. Each of these businesses deals in substantially complicated, and typically large, insurance policies for which specialty knowledge is required and an experienced market like Lloyd's is essential.

        The London market is also a center of our reinsurance brokerage operations. The reinsurance brokerage industry developed in London in the late 1800s, with a principal contributor being Cuthbert Heath, the "Founder of Modern Lloyd's." Reinsurance brokerage facilitated expansion of Lloyd's insurers into foreign markets at the turn of the twentieth century by allowing them to alleviate their risks in unfamiliar social and political geographies. London reinsurance brokers continue to be the principal developers of emerging markets, particularly in Eastern Europe and Asia. Aon Re already had substantial London business operations when it acquired UK-headquartered Benfield—at the time the world's third-largest reinsurance broker—to create the preeminent reinsurance brokerage firm in the world. Benfield's corporate ancestry dates back to the founding of W.T. Greig Ltd. in 1921, the company credited as the principal innovator of the London reinsurance brokerage industry with its development of catastrophic analytics and overseas expansion. Aon Re is therefore well positioned in the important London market where a disproportionate amount of Aon Re's business continues to be placed for non-UK and UK clients. London is a critical reinsurance center both because of the large number of clients based in London as well as the presence of specialist capability which means a disproportionate amount of business is placed through London.

        The United Kingdom is also a central location for our HR Solutions business. Throughout the 2000s, the business associated with HR Solutions, under the Hewitt name, acquired a number of companies with substantial operations in London. In 2000, Aon acquired Bacon & Woodrow, the third-largest employee benefits consulting firm in the U.K. By 2003, over 10% of Hewitt's employees were located in the U.K. In 2004, Hewitt made its largest acquisition, the purchase of Exult Inc., a publically-traded company specializing in multi-process HR Outsourcing (now called HR BPO). Exult's international headquarters were located in the U.K., and its core HR BPO service lines, such as payroll and HR information systems, were natural adjacencies to Hewitt's core benefits business. This acquisition accelerated Hewitt's existing market presence both within the HR BPO space as well as internationally through the London presence. In 2008, Hewitt acquired New Bridge Street Consultants, a U.K. based consultancy that assists companies in designing and implementing remuneration policies that help them meet their strategic goals. As a result of these acquisitions, London has been established as a key international market for each of HR Solutions' business lines of consulting, benefits administration and HR BPO.

        In 2010, Aon Hewitt earned $4.5 billion in revenue on a pro forma basis. Of this amount, roughly $2.2 billion is from Aon Hewitt's Benefits Administration and BPO businesses and $2.3 billion is from its consulting business. Of the $2.3 billion in consulting revenues, $1.2 billion is earned internationally and over $400 million was earned in the U.K.

        Overall, our U.K. business accounted for approximately 15.5% of our 2010 revenue.

Expansion of our Global Presence

        Over the last 20 years, Aon has transformed its profile from a US-centric firm to a more global professional services firm. Our revenue mix from international operations has increased significantly during this period—from 13% of global revenues in 1990 to 52% of global pro forma revenues in 2010.

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        Aon drives its capital decision making process around return on invested capital, firmly believing this methodology has a higher correlation than any other metric with creation of shareholder value. In this regard:

•

Beginning in 2006, we began to simplify our global organization and execute on a strategy to exit lower margin and more capital intensive insurance underwriting businesses.



•

From 2006 to 2009, Aon divested significant non-core assets including: Aon Warranty Group, Construction Program Group, Sterling Life Insurance, and Combined Insurance Companies of America, each of which had substantial US operations.



•

The successful exit of the low margin, capital intensive insurance underwriting businesses and non-core assets strategically eliminated 23% of the company's total revenue in 2006.

        Then, with the acquisitions of Benfield Group in 2008 and Hewitt Associates, Inc. in 2010, Aon successfully transformed its portfolio to higher-margin, capital-light professional services businesses with 75% of revenues in Risk Solutions and 25% of total revenues in HR Solutions, resulting in high recurring revenue streams and strong free cash flow generation characteristics. For the nine months ended September 30, 2011, 60% of our revenues were earned by Risk Solutions and 40% by HR Solutions. Aon expects to experience a growing international presence in both segments.

Reasons for the Merger

        The merger is part of a reorganization of Aon's corporate structure, which includes a change of our place of incorporation from Delaware to the U.K., where we already have substantial operations, and the relocation of several key executive officers with global responsibilities to London.

        We believe the reorganization will strengthen our long-term strategy by:

•

Enhancing our focus on growth by positioning our resources more proximately to the geographic areas poised to experience the highest level of expansion and which areas today derive a substantial portion of their risk coverage through the U.K. market;



•

Enabling our Risk Solutions business to deliver superior value to our clients and differentiate us from our competition via key retail initiatives that are or will be substantially driven from the U.K., such as GRIP, Programs & Facilities and Broking Excellence and key reinsurance initiatives that are or will be substantially driven from the U.K., such as facultative programs and further expanding our Aon Re Analytics capabilities;



•

Allowing us to expand the penetration of our HR Solutions segment into Europe through London, the current base for much of our European consulting operations and growing our U.K. and EMEA benefits administration and HR BPO business lines;



•

Leveraging our development, retention and acquisition of professional talent and optimizing its geographic deployment around the world in each of our primary and developing markets;



•

Optimizing our fiscal planning and capital allocation and reducing our global tax rate in a manner that provides us with increased financial flexibility to properly invest in our growth, Risk Solutions product innovation, HR Solutions expansion and talent development strategies while delivering increased shareholder value as follows:



•

Providing greater global access, as a result of the U.K.'s tax rules regarding the repatriation of earnings, to expected increases in future cash flow as Aon delivers on its long-term operating margin targets while certain required uses of cash decrease over the next several years as restructuring costs decline and contributions to our material pension plans that are closed to new entrants and, where statutorily permitted, frozen from continued benefit accruals are reduced, as those plans become more fully funded;

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•

Enabling us to access approximately $300 million of excess capital held internationally on our balance sheet upon consummation of this reorganization;



•

Increasing future cash flows through a significant reduction in our global tax rate over the long term due to changes in the geographic distribution of income, similar to the reduction achieved over the last five years, which would allow us to remain competitive with certain global competitors; and



•

Delivering increased shareholder value as we effectively allocate capital through share repurchases and dividends.

Growth

        We expect our revenues outside of North America to increase as a proportion of our overall revenues and we believe that this growth will come disproportionately from Latin America, Asia, Africa and Eastern Europe, and is correlated with growth in insurance premium penetration, increased need for broad based human resources solutions, higher GDP growth and high employment rates.

        The reorganization is intended to position our company to further benefit from these growth opportunities and allow our management to more effectively implement our global strategy and increase our focus on customer development in these areas by positioning more resources closer to these areas. In this regard, we also expect that the reorganization will result in operational and administrative efficiencies over the long term and enhance our ability to expand in the U.K., Europe and internationally, while maintaining our focus on our critical U.S. market as well as better serving our large U.S. multinational customers.

Risk Solutions

        Our broking strategies are expected to drive growth in our Risk Solutions business through product and broking innovations such as the Global Risk Insight Platform, Programs & Facilities, retail Broking Excellence, and reinsurance broking. In particular:

•

Our GRIP product offers world class benchmarking for all complex or large risks placed through the London market. Through continually enhancing and expanding these GRIP activities with our Lloyd's carriers, we can continue to develop new products and best in class broking solutions for our clients.



•

Our broking activities in London are key to our Programs & Facilities strategy as they allow us to continually provide innovative best in class solutions underwritten out of London to address new and existing risks for our clients at the right price with the best coverage. These solutions often need the capacity of the London market and the capability of the people to design and develop such facilities in a way that meet the global needs of the network offices serving local clients.



•

Our retail Broking Excellence strategy is centered out of our Global Broking Centre ("GBC") in London providing solutions in the many specialist lines and wholesale markets for our global clients' large and complex risks. Expanding and investing in the capability and expertise in the GBC is critical to our ability to continue delivering these best in class program design solutions within this Broking Excellence strategy. Residing close to Lloyd's enables access to both the talent resource pool and specialist capability that is needed to achieve this.



•

Our reinsurance broking strategy depends heavily on the expertise and specialist knowledge provided by the Lloyd's market and London based capital providers of global reinsurers. It is essential we utilize this specialist capability and London talent to be able to innovate and deliver

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robust solutions and analytics that meet our insurance and reinsurance clients' business strategy needs and their balance sheet protection needs.

        To efficiently develop these innovations for clients, there is a need for their supporting teams to be close to Lloyd's of London and the specialist capability and talent that exists among Aon's UK brokers. London has historically been a global center for training brokers, and Benfield has a long-standing tradition for training reinsurance brokers from brokerage firms in Asia, Europe and the United States. As a result, teams responsible for developing and supporting these innovations are centered in London. We expect that locating more executive resources in London will increase and improve our access to the insurance markets there as well as appropriately leveraging our technical capabilities and talent in the London office.

HR Solutions

        Through our HR Solutions business we expect to be a leading consulting and benefits outsourcing service provider in all markets in the world. London is a key market for each of the Aon Hewitt business lines of consulting, benefits administration and HR Business Process Outsourcing. Within the consulting line, London is the base for the European business which governs emerging Eastern European, Middle Eastern and African markets where Aon Hewitt has identified future growth potential. The retirement benefits consulting industry is similarly based out of London, with substantial Aon Hewitt human capital working with key European and global clients. The investment consulting business is also headquartered in London, with research and data analytics being performed for pension plans around the world. London is also a key market for the global benefits administration and business process outsourcing business. Administration of retirement and flexible benefits, the largest line of business in the administration industry, is principally performed out of London for all of Europe, and back office functions performed in Poland are directed out of London.

Talent Development and Deployment

        We believe that a substantial investment in talent development across Aon will be central to our success over the next twenty years. A considerable effort is already underway, entitled "Aon United Talent." This initiative establishes a global approach to talent development, retention and acquisition. Being the "destination of choice" for the best talent in Risk and HR is fundamental to our delivering the best professional services to clients. This effort will also result in additional hiring and investment in offices of regional significance to Aon, including London, Chicago and Singapore.

        Given the importance of London and the U.K. to our business, we already have several key senior executives who are located there or have been trained in our London office. As a result of this reorganization, certain additional key senior executive positions are expected to relocate to London. Our London office will continue to be a global training center for our executives and brokers, as well as our Chicago and Singapore offices. We expect that having more senior executives located in a more central location will permit them to coordinate and interact with worldwide operations during their normal business hours, and improve executive oversight of these operations.

Financial Flexibility

        The reorganization will provide the additional benefit of allowing us the opportunity to optimize our fiscal planning and capital allocation in a manner that allows us to better utilize our capital, including to support and further enable our strategies to drive future growth, enhance product innovation in our Risk Solutions segment, expand the geographic reach of our HR Solutions segment, and spur talent development. It will create financial flexibility for us in four primary ways:

•

The reorganization will provide us with greater global access, as a result of the U.K.'s tax rules regarding the repatriation of earnings, to expected increases in future cash flow as Aon delivers

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on its long-term operating margin targets while certain required uses of cash decrease over the next several years; as restructuring costs decline and contributions to our material pension plans that are closed to new entrants and where statutorily permitted, frozen from continued benefit accruals, are reduced as those plans become more fully funded.

•

Upon its consummation, the reorganization will also allow us to access approximately $300 million of excess capital held internationally on our balance sheet.



•

We expect that due to changes in the geographic distribution of our income after the reorganization, future cash flows should increase as our global tax rate is significantly reduced.



•

The improvement in capital allocation should enable us to deliver increased shareholder value through share repurchases and dividend distributions.

        While we expect that the reorganization should improve our financial flexibility along these lines, we cannot give any assurance as to what the scope or magnitude of the improvement in our capital position will be after the reorganization. Nor can we give any assurances that tax laws in the U.K. or the U.S. will not be modified or interpreted in a manner that adversely impacts our ability to avail ourselves of these benefits.

        While the reasons set forth above were the principal rationale for our Board's approval of the reorganization, the Board also took into account that the U.K. is a major financial center known for its stability and financial sophistication and that the U.K. has a stable and well-developed legal system that we believe encourages high standards of corporate governance and provides shareholders with substantial rights. See "Description of Class A Ordinary Shares of Aon UK," and "Comparison of Rights of Stockholders/Shareholders."

        In approving the merger, our Board was also cognizant of and considered a variety of negative or potentially negative factors, including the possibility that the uncertainty created by the relocation of our legal domicile and potential negative press coverage associated with that relocation and relocation of certain key executives could create uncertainty among our colleagues in the U.S. generally, and Chicago, specifically; the possibility that such negative coverage could make some of our clients, particularly those in the U.S., reluctant to do business with us; the capital gains tax that will affect some of our stockholders; the fact that we expect to incur costs to complete the reorganization, including the costs to relocate colleagues to the U.K., and the costs to further invest in our U.K. presence; the fact that U.K. corporate law imposes additional obligations on the Company and that compliance with applicable U.K. corporate regimes will result in increased costs worldwide; the diversion of management's time and attention; and the fact that the expected benefits of the reorganization may not be realized for a variety of reasons or delayed for a significant period of time, including as a result of authorities disagreeing with our conclusions on tax treatment or changing applicable tax laws and regulations with potentially retroactive effect.

        In the course of its review of the reorganization and its attendant risks, our Board engaged in discussions with management and external advisors to evaluate and determine methods to mitigate potentially negative consequences of the reorganization. Please see "Cautionary Statement Concerning Forward-Looking Statements" and "Risk Factors" for further discussion of the negative and potentially negative factors discussed above and for a discussion of factors that could prevent us from achieving the benefits described above that we anticipate from completion of the reorganization.

        After completing its process of review of the expected benefits and potential risks, our Board determined, with its members Edgar J. Jannotta, Andrew J. McKenna and John W. Rogers, Jr. abstaining and each of the other members of the Board voting in favor, that the merger, the reorganization and the passage of each of the proposals contained in this proxy statement is in the best interests of Aon Delaware and its stockholders and to recommend that Aon Delaware stockholders

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should vote in favor of the adoption of the merger agreement and each of the other proposals contained in this proxy statement.

The Merger

        The steps that have been taken to date, and that will be taken, to complete the merger are:

•

Aon Delaware formed Aon UK as an English private limited company, with Class A Ordinary Shares and Class B Ordinary Shares.



•

Aon Delaware deposited the Class A Ordinary Shares of Aon UK with EES. Aon Delaware and EES entered into a depositary agreement governing the deposit of the Class A Ordinary Shares with EES. Aon Delaware continued to hold the Class B Ordinary Shares.



•

Aon Delaware formed Aon Intermediate as a Delaware limited liability company and a direct wholly-owned subsidiary of Aon Delaware.



•

Aon Intermediate formed Aon Mergeco as a Delaware corporation and a direct wholly-owned subsidiary of Aon Intermediate.



•

Aon Delaware and Aon Mergeco entered into the merger agreement;



•

The stockholders of Aon Mergeco adopted and approved the merger agreement;



•

Aon Delaware and Aon Intermediate entered into a contribution agreement whereby Aon Delaware agreed that, conditional upon the effectiveness of the registration statement of which this proxy statement/prospectus is a part, Aon Delaware will contribute all of its interests in the Class A Ordinary Shares to Aon Intermediate. Aon Intermediate and Aon Mergeco entered into a contribution agreement whereby Aon Intermediate agreed that, conditional upon its receiving such interests in the Class A Ordinary Shares, Aon Intermediate will contribute all of its interests in the Class A Ordinary Shares to Aon Mergeco.



•

Aon Delaware and Aon UK entered into a contribution agreement whereby Aon Delaware agreed that, conditional upon approval of the merger agreement by its stockholders, Aon Delaware will contribute all shares of Aon Intermediate to Aon UK.



•

Prior to the effective time of the merger, Aon UK will re-register as a public limited company and change its name to "Aon plc" or a similar name.



•

A special resolution of Aon UK will be passed to alter the rights of the holders of the Class A Ordinary Shares to have the same rights as holders of Class B Ordinary Shares, conditional upon the merger becoming unconditional in all respects.



•

After the stockholders of Aon Delaware approve the adoption of the merger agreement, Aon Delaware will contribute all shares of Aon Intermediate to Aon UK.



•

When the merger becomes effective,



•

Each share of Aon Delaware common stock (other than treasury shares) will be converted by operation of law into and become the right to receive one Class A Ordinary Share. This will result in each holder of Aon Delaware common stock receiving one Class A Ordinary Share for each share of Aon Delaware common stock held immediately prior to the merger;



•

Each holder of Aon Delaware common stock exchanged in the merger who would otherwise have received a fraction of a Class A Ordinary Share will receive cash in an amount determined by multiplying the fractional interest to which such holder would otherwise be entitled by the closing price for a share of Aon Delaware common stock as reported on the New York Stock Exchange on the last trading day prior to the effective time of the merger. All fractional interests to which a single holder would be entitled shall be aggregated and calculations shall be rounded to three decimal places. Any cash payment in exchange for a fractional interest will be made in U.S. dollars and will be rounded to the nearest cent; and



•

Each issued share of Aon Mergeco will be converted by operation of law into one share of Aon Delaware (as the surviving corporation), which will be held by Aon Intermediate.

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•

The Class A Ordinary Shares shall have been deemed eligible for deposit, book-entry and clearance services by DTC and its affiliates;



•

In addition, all shares of Aon Delaware common stock held in treasury immediately prior to the merger will automatically be cancelled and retired and will cease to exist, without consideration being delivered for such cancellation and all Class B Ordinary Shares of Aon UK will remain outstanding, but will have no voting rights or rights to dividends or distributions to the extent that they are held by Aon Delaware.



•

Each outstanding option, share of restricted stock and other equity-based award issued under our equity incentive plans for the purchase or receipt of, or benefits or amounts based on, shares of Aon Delaware common stock will represent the right to purchase or receive, or receive benefits or amounts based on, as applicable, the same number of Class A Ordinary Shares of Aon UK on the same terms.



•

Aon Mergeco or Aon Delaware as the surviving corporation will cause the Class A Ordinary Shares to be delivered to the Aon Delaware stockholders.

        The merger agreement may be amended, modified or supplemented at any time by the parties thereto before or after it is adopted by the stockholders of Aon Delaware. However, after adoption by the stockholders, no amendment, modification or supplement may be made or effected that requires further approval by Aon Delaware stockholders without obtaining that approval. Further, our Board may abandon the merger at any time, including after stockholder approval.

Ownership in Aon UK; Conversion of Shares; Delivery of Shares to Former Record Holders

        The conversion of Aon Delaware common stock into the right to receive the merger consideration will occur automatically at the effective time of the merger. The exchange agent will, as soon as reasonably practicable after the effective time of the merger, exchange certificates representing Aon Delaware shares for the merger consideration in the form of Class A Ordinary Shares to be received in the merger pursuant to the terms of the merger agreement, including the receipt of certificates and properly executed letter of transmittal, where applicable. The interests in the Class A Ordinary Shares will be contributed to Aon Mergeco prior to the effective time of the merger and, following the effective time of the merger, the Class A Ordinary Shares will be delivered to the exchange agent through the facilities of DTC for credit to Aon Delaware stockholders upon surrender of the certificates representing Aon Delaware common stock.

        If you are currently a beneficial holder of Aon Delaware common stock (i.e., your shares are held in "street name"), your ownership of Class A Ordinary Shares will be recorded in book entry form by your broker on the effective date of the merger.

        All other Class A Ordinary Shares delivered in connection with the merger will also initially be delivered through the facilities of DTC. If you hold share certificates representing Aon Delaware shares or if you otherwise hold Aon Delaware shares as record holder, your Class A Ordinary Shares will initially be delivered to the Custodian, as custodian for you. Any such shares will be evidenced by a statement issued by the Custodian. No former record holder of Aon Delaware whose Class A Ordinary Shares are delivered to the Custodian will be required to pay any fees to the Custodian for the initial 90 day period. Any such holder who wishes to transfer its shares from the custody of the Custodian to another bank or broker or to receive certificated Class A Ordinary Shares will not be charged any fees to do so by the Custodian or Aon UK.

        Following the effective time, such former record holders of Aon Delaware will be provided with terms and conditions governing their custody account and must provide the Custodian with "know your customer" information and other customary documentation and must agree to the terms and conditions if they wish the custodian to continue holding their Class A Ordinary Shares. If a former record holder

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does not provide such documentation within 90 days of the effective time of the merger, its shares will be debited from its custody account with the Custodian and it will be issued a certificate in respect of its Class A Ordinary Shares by the Company or its transfer agent or registrar, and it will subsequently hold your shares of Aon UK as a registered or record shareholder. Certain non-U.S. shareholders will not be eligible to hold their shares through the Custodian after the initial 90 day period. Any such shareholders who do not inform the Custodian of another bank or broker to whom their shares should be transferred prior to the end of the initial 90 day period will be issued shares in certificated form.

        Transfers of shares by record holders of the Company (including a transfer of shares to a broker-dealer or other nominee or a private transfer between individuals on the register) will generally attract stamp duty or stamp duty reserve tax, or "SDRT" under U.K. law. For more information, see "Material Tax Considerations Relating to the Merger—Material U.K. Tax Considerations Relating to and After the Merger—Stamp Duty and SDRT". As a result, if a former record holder of shares of Aon Delaware does not provide the Custodian with "know your customer" and other customary information in respect of shares delivered in connection with the merger within 90 days of the effective time, such a holder will be issued a certificate and will not be able to transfer those shares into DTC without incurring stamp duty and/or SDRT. As a result, each former record holder is strongly encouraged to provide the information requested by the Custodian in a timely manner, so the shares may remain within the facilities of DTC.

        If you hold Aon Delaware stock certificates, soon after the effective time of the merger, you will be sent a letter of transmittal, which is to be used to surrender your Aon Delaware stock certificates and to request that Class A Ordinary Shares be delivered to you. The letter of transmittal will contain instructions explaining the procedure for surrendering Aon Delaware stock certificates and receiving Class A Ordinary Shares, which shall initially be issued to the Custodian noted above in non-certificated book entry form. The letter of transmittal will specify that delivery shall be effected, and risk of loss and title to Aon Delaware stock certificates shall pass, only upon actual and proper delivery of the certificates to the exchange agent. Only those certificated holders of Aon Delaware common stock who properly surrender their common stock certificates in accordance with the instructions contained in the letter of transmittal will receive Class A Ordinary Shares and cash in lieu of any fractional interests. YOU SHOULD NOT RETURN STOCK CERTIFICATES WITH THE ENCLOSED PROXY CARD. If a certificate for Aon Delaware common stock has been lost, stolen or destroyed, the exchange agent will issue the merger consideration properly deliverable under the merger agreement upon compliance by the applicable stockholder with the replacement requirements established by the exchange agent. After the effective time, each certificate representing shares of Aon Delaware common stock that has not been surrendered will represent only the right to receive upon surrender of that certificate, the Class A Ordinary Shares and cash in lieu of fractional interests, if any, to which such holder is entitled. Following completion of the merger, Aon Delaware will not register any transfers of Aon Delaware common stock outstanding on its stock transfer books prior to the merger.

Dividends and Distributions; Withholding; Termination of Exchange Fund; No Liability

        Until Aon Delaware stock certificates or book-entry shares are surrendered for exchange, any dividends or other distributions of Aon UK declared after the effective time of the merger with respect to Class A Ordinary Shares will accrue but will not be paid. Aon UK will pay to former Aon Delaware stockholders any unpaid dividends or other distributions, without interest, only after they have duly surrendered their Aon Delaware stock certificates or book-entry shares. After the effective time of the merger, there will be no transfers on the stock transfer books of Aon Delaware of any Aon Delaware shares. If stock certificates representing Aon Delaware shares are presented for transfer after the completion of the merger, they will be cancelled and exchanged for the merger consideration into which the Aon Delaware shares represented by that certificate have been converted.

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        The exchange agent will be entitled to deduct and withhold from the merger consideration payable to any Aon Delaware stockholder the amounts it is required to deduct and withhold under the Code or any provision of any state, local or foreign tax law. If the exchange agent withholds any amounts, these amounts will be treated for all purposes of the merger as having been paid to the stockholders from whom they were withheld.

        Any portion of the securities or funds deposited with the exchange agent that remain undistributed to the former holders of shares of Aon Delaware common stock at the twelve month anniversary of the effective time of the merger will be delivered to Aon Delaware, as the surviving corporation, upon demand, or to its designee, and any former holder of shares of Aon Delaware common stock who has not theretofore properly surrendered its stock certificates shall thereafter look only to Aon Delaware, as the surviving corporation, for payment of any consideration due to it hereunder.

        None of Aon Delaware, Aon UK or the exchange agent will be liable to any former holder of shares of Aon Delaware common stock for any securities properly delivered or any amount properly paid by the exchange agent or its nominee, as the case may be, to a public official pursuant to applicable abandoned property, escheat or similar law nine months after the effective time of the merger. If any certificate representing shares of Aon Delaware common stock has not been surrendered prior to two years after the effective time of the merger (or immediately prior to an earlier date on which the Class A Ordinary Shares in respect of the stock certificate would otherwise escheat to or become the property of any governmental entity) any cash, share dividends and distributions otherwise payable in respect of the certificate shall, to the extent permitted by applicable law, become the property of Aon Delaware, as the surviving corporation, free and clear of all claims or interest of any person previously entitled thereto.

Subsequent Actions

        The merger is part of a reorganization of Aon Delaware's corporate structure. Following the consummation of the merger, Aon UK, as Aon Delaware's ultimate parent company, expects to examine various potential transactions that could bring about a further repositioning of the organizational structure of Aon Delaware and certain of its subsidiaries and their respective assets, in order to achieve the benefits of the reorganization described above under "—Background and Reasons for the Merger." We refer to these activities and transactions in this proxy statement/prospectus as "subsequent actions."

Possible Abandonment

        Pursuant to the merger agreement, the Board may exercise its discretion to terminate the merger agreement, and therefore abandon the reorganization, at any time, including after stockholder approval. Please see "Risk Factors—Our Board may choose to defer or abandon the merger at any time."

Additional Agreements and Actions

        The "Comparison of Rights of Stockholders/Shareholders—Indemnification of Directors and Officers" sets out the position under English law in relation to director and officer liability and indemnification. We expect to enter into new indemnity agreements and deeds of indemnity with directors, executive officers and certain other officers and employees (including directors, officers and employees of subsidiaries and other affiliates). These indemnification agreements and deeds of indemnity will require that Aon UK indemnify and hold harmless such persons, to the fullest extent permitted by applicable law, against all losses suffered or incurred by him or her which arise in connection with his or her appointment as a director or officer, as applicable, an act done in connection with his or her performance of his or her functions as a director or officer or an official investigation ordered into the affairs of the company of which he or she is serving as a director or

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officer at the request of the indemnifying company. However, the Companies Act prohibits an English company from indemnifying directors and certain officers in particular circumstances which are set out in the relevant indemnity agreements and generally summarized in the "Comparison of Rights of Stockholders/Shareholders—Indemnification of Directors and Officers."

        The reorganization does not constitute a change in control for purposes of Aon Delaware's equity incentive plans and change in control severance agreements. We have amended and/or intend to amend the equity incentive plans, change in control severance agreements and certain other plans and agreements, as necessary or advisable and to the extent permitted, to provide that any outstanding equity award is converted into rights to Class A Ordinary Shares on an equivalent one-share to one-share basis as of the effective time of the merger and to provide that the reorganization will not constitute a change in control under the terms of the applicable plans or agreements. Please see below "—Stock Compensation and Benefit Plans and Programs." Certain of our executive officers who will relocate to London following the merger had protection in their employment agreements that allowed them to terminate such agreements and receive severance benefits for "good reason" on account of their required relocation. Each executive officer that would have been entitled to such a termination in connection with the merger has consented to his or her international assignment and waived such severance protection in connection with his or her assignment and repatriation thereafter.

        In connection with the consummation of the reorganization, we do not expect any material actions to be required with respect to our (i) 8.205% junior subordinated deferrable interest debentures due January 2027, which have an aggregate principal amount outstanding of $687.0 million as of September 30, 2011, (ii) 6.25% €500 million debt securities due July 2014, which have an aggregate principal amount outstanding of €500 million as of September 30, 2011, (iii) 5.00% senior notes due September 2020, which have an aggregate principal amount outstanding of $600 million as of September 30, 2011, (iv) 3.50% senior notes due September 2015, which have an aggregate principal amount outstanding of $600 million as of September 30, 2011, (v) 5.05% CAD 375 million debt securities due April 2011, which have an aggregate principal amount outstanding of CAD 375 million as of September 30, 2011, (vi) 6.25% senior notes due September 2040, which have an aggregate principal amount outstanding of $300 million as of September 30, 2011, and (vii) 7.375% debt securities due December 2012, which have an aggregate principal amount outstanding of $225 million as of September 30, 2011. However, we intend to enter into supplemental indentures and other amendments as necessary or advisable to provide for guarantees by Aon UK or certain of its subsidiaries in connection with the reorganization. We will also provide financial information regarding Aon Delaware in the manner required by the aforementioned instruments. Refer to "Forward-Looking Statements" and "Risk Factors" above for a description of certain risks associated with the reorganization.

        We have a $450 million unsecured term loan facility (the "US Term Facility") with a syndicate of lenders, the proceeds of which were used to refinance a prior term loan facility. The US Term Facility matures in October 2013 and as of September 30, 2011, $438.8 million was outstanding under the US Term Facility.

        We also have a $400 million unsecured revolving credit facility (the "US Revolving Facility") and a €650 million unsecured revolving credit facility (the "Euro Revolving Facility"), with syndicates of lenders for general corporate purposes. The US Revolving Facility matures in December 2012 and the Euro Facility matures in October 2015. As of the date of this proxy statement/prospectus, there were no amounts outstanding under the US Revolving Facility and there were no amounts outstanding under the Euro Revolving Facility.

        In connection with the reorganization, we expect to seek the amendment or waiver of certain provisions of, or to renegotiate the terms of, the US Term Facility, the US Revolving Facility and the Euro Revolving Facility. If we are unsuccessful in modifying these credit facilities by the effective time of the merger, we may be in breach of certain provisions of these credit facilities.

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Conditions to Completion of the Merger

        Unless, among other things, the following conditions or requirements are satisfied or, if allowed by law, waived, the merger, and therefore the reorganization, will not be completed:

•

upon the SEC's declaration of effectiveness of the registration statement on Form S-4 with respect to the merger, Aon Delaware will have contributed all interests in the Class A Ordinary Shares to Aon Intermediate, which will in turn have contributed all such interests in the Class A Ordinary Shares to Aon Mergeco;



•

the merger agreement will have been adopted by the requisite vote of Aon Delaware stockholders;



•

Aon UK will have re-registered as a public limited company;



•

following stockholder approval of the merger agreement, Aon Delaware will have contributed all shares of Aon Intermediate to Aon UK;



•

a special resolution will have been passed to alter the rights of the holders of the Class A Ordinary Shares to have the same rights as holders of Class B Ordinary Shares, nominal value £0.10 each, or "Class B Ordinary Shares," conditional upon the merger becoming unconditional;



•

the Class A Ordinary Shares will have been authorized for listing on the NYSE, subject to official notice of issuance and satisfaction of other standard conditions;



•

the Class A Ordinary Shares shall have been deemed eligible for deposit, book-entry and clearance services by The Depository Trust Company and its affiliates;



•

McDermott Will & Emery LLP, legal counsel to Aon Delaware, will have delivered a tax opinion in form and substance acceptable to Aon Delaware;



•

no decree, order or injunction will have been in effect with respect to the SEC registration statement of which this proxy statement/prospectus is a part;



•

other than the filing of the certificate of merger with the Secretary of State of Delaware in connection with the merger, all material consents and authorizations of, filings or registrations with, and notices to, any governmental or regulatory authority required of Aon Delaware, Aon Mergeco or any of their respective subsidiaries to consummate the merger and the other transactions contemplated by the merger agreement, including without limitation any consents, authorizations, filings or registrations required under (i) applicable U.S. state securities and "Blue Sky" laws, (ii) U.K. financial services laws, and (iii) laws governing insurance brokerage in various countries in which we do business, shall have been obtained or made; and



•

none of the parties to the merger agreement shall be subject to any decree, order or injunction of any court of competent jurisdiction, whether in the U.S., the U.K., the European Union or any other country, that prohibits the consummation of the merger.

        Our Board does not intend to waive (where capable of waiver) any of these conditions or requirements unless it determines that the merger is in the best interests of Aon Delaware and our stockholders, despite the condition(s) not being satisfied in whole or in part. Notwithstanding the foregoing, our Board reserves the right to defer or abandon the merger at any time, including after stockholder approval, for the reasons described under "Risk Factors—Our Board may choose to defer or abandon the merger at any time."

        Approval of the reduction of capital of Aon UK and the approval of the relocation compensation in the advisory, non-binding vote described in this proxy statement/prospectus are not conditions to the completion of the merger.

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