Aon to acquire Benefield Group Limited

Transaction Creates Premier Reinsurance Franchise with Global Reach, Diverse Product Capability and World Class Colleagues to Serve Clients’ Evolving Needs

CHICAGO AND LONDON, 22 August 2008 – Aon Corporation (NYSE: AOC) and Benfield Group Limited (LSE: BFD) announced that the boards of directors of both companies have unanimously approved a definitive agreement under which Aon will acquire Benfield for £3.50 ($6.55) per share in cash and assume £91 million ($170 million) of Benfield net debt, representing an enterprise value of approximately £935 million ($1.75 billion) on a fully diluted basis. The consideration represents a 29 percent premium to Benfield’s closing stock price on August 21, 2008, the last trading day prior to the announcement of the agreement.

Benfield is a leading independent reinsurance intermediary in terms of reputation and standing. The Benfield business is renowned in the industry for its excellent client service, leading analytics capability and record of innovation. Aon believes that, as part of Aon Re Global, Benfield can continue to build upon these strengths, creating an unparalleled reinsurance franchise with global reach, diverse product capability and world class colleagues to effectively serve clients’ evolving needs. Following the close of the transaction, Aon intends to integrate the Benfield business with its existing reinsurance operations (Aon Re Global) and operate the division globally under the newly created Aon Benfield Re brand.

“This agreement reflects our ongoing efforts to ensure that Aon’s colleagues, capabilities and technology remain at the forefront of our industry and that we provide the best value for our clients,” said Greg Case, president and chief executive officer of Aon Corporation. “Over the past several years, we have made significant progress in strengthening Aon’s operational platform and global network, becoming a more client-focused organization with a broader portfolio of innovative products and services. With Aon Benfield Re, we will build on this progress to further enhance organic growth, expand margins, and drive shareholder value.”

Mr. Case continued, “Aon and Benfield share a common focus on excellence in client service, and both recognize the importance of being the destination of choice for the best talent in our industry. The strong cultural fit between our firms will enable us to quickly realize the benefits of this transaction, and the value added for our clients and shareholders, in a seamless fashion following the close of our transaction.”

Grahame Chilton, chief executive officer of Benfield, commented, “We are excited by this unique opportunity to create a powerful global franchise capable of expanding and redefining innovative reinsurance and capital market solutions. At the same time, the Benfield board believes that the offer provides Benfield’s shareholders with fair and certain value. We look forward to joining the Aon team and working with them as Aon Benfield Re to expand our joint expertise and local reach to customers around the world.”

“I have significant respect and admiration for the Benfield organization,” noted Michael O’Halleran, executive chairman of Aon Re Global. “I look forward to working with Grahame, Andrew and our colleagues and team members as we combine the strengths of our two organizations into the leading reinsurance and capital management advisor in the world.”

Andrew Appel, chief executive officer of Aon Re Global, added, “The combination of our two firms will create an unparalleled set of capabilities to deliver distinctive client value, drive innovation in analytics and capital management, and enhance the value proposition for colleagues and team members in both businesses.”

Benefits of the Transaction

Aon’s and Benfield’s reinsurance operations are highly complementary. Through the transaction, Benfield will add significantly to capabilities in:

· Developing markets around the world that both firms have targeted for growth, including Asia, Central and Eastern Europe, Africa and Latin America. Benfield’s reputation for its long-standing client relationships in Japan and other Asian markets, in particular, is extremely strong;

· Global analytics, modelling and client facing technology, which have enabled Benfield to differentiate itself in the marketplace, as demonstrated by its achievement of significant market share as well as the receipt of numerous industry awards, including 12 awards received in 2007 and 2008 alone;

· The U.S. Florida and South East property-catastrophe markets, where Benfield’s pioneering ReMetrics capability, together with its long-standing market experience, deliver to clients a uniquely attractive risk analysis proposition;

· Key major accounts. On a pro forma basis, Aon Benfield Re will serve the majority of insurance and reinsurance carriers globally. Aon expects the new and expanded client relationships afforded by the combination to support continued growth;

· Cost savings and operational efficiencies. The transaction is expected to generate approximately £65 million ($122 million) in annual cost savings fully phased-in in 2011, primarily from shared administrative and support services across both Aon Re Global and Benfield;

· Strong operating cash flows. Aon expects strong operating cash flows following the transaction to continue to support the Company’s capital allocation priorities including, among others, its share repurchase program. As of August 7, 2008, Aon has repurchased 89.8 million of its shares for $3.7 billion and had approximately $900 million remaining under its share repurchase authorization. Aon plans to complete the remaining share buyback by year-end 2009.

The return on invested capital (ROIC) on the acquisition is 13.8 percent compared to 12 percent on the share repurchase program.

Transaction Summary

The transaction is expected to close by the end of 2008, subject to customary closing conditions and regulatory approvals as well as approval by Benfield shareholders. Aon has received commitments from Benfield shareholders representing approximately 25.4 percent of Benfield’s outstanding shares to vote their shares in favor of the transaction.

Aon intends to fund the transaction through cash on hand. The transaction is not subject to a financing contingency.

Aon expects the acquisition to be accretive to earnings per share in the first year after closing, excluding one-time items, and meaningfully accretive thereafter.

Following the close of the transaction, Grahame Chilton, chief executive officer of Benfield, will serve as vice chairman of Aon Group, reporting to Greg Case, chief executive officer, Aon Corporation. Mr. Chilton will join the Aon Corporation executive committee and the Aon Benfield Re executive committee. Michael O’Halleran and Andrew Appel will serve as executive chairman and chief executive officer, respectively, of Aon Benfield Re. Mr. Appel will continue to serve as chairman, Aon Consulting Worldwide.

Exchange Rate

GBP/USD: 1.87.