The City's chief regulator signalled a crackdown on bribery on Thursday as it fined one of the biggest insurance brokers £5.25 million for anti-corruption failings.

Aon Limited, a subsidiary of Aon Corporation, the risk management and insurance group, was found to have made numerous suspicious payments over a two-and-a-half-year period from early 2005 to late 2007.

The fine was the first levelled against a company for failing to crack down on possible bribery and the sixth largest meted out by the Financial Services Authority.

The transactions, including two specific payments of €1.4 million (£1.26 million) and $3.25 million (£2.13 million) to unnamed third parties, were made as part of Aon's efforts to win business overseas.

Like many insurers operating overseas, Aon employed “introducers” to help generate new business. The two specific payments involved a Bulgarian insurance company and a company owned by the Burmese Government, respectively.

Aon admitted that it could not confirm that the payments were legitimate.

Peter Harmer, Aon's chief executive in the UK, said: “We did not have appropriate systems and controls in place to identify and assess the risks involved in making payments to third parties. We could not provide certainty.” Internal controls were now among the best in the industry, he added.

The fine would have been £7.5 million but for Aon's co-operation and willingness to settle at an early stage.

Aon Limited made 66 suspicious payments to win or retain business in Bahrain, Bangladesh, Bulgaria, Burma, Indonesia and Vietnam, the FSA said. The payments, discovered in 2007, were reported to the Serious Organised Crime Agency.

Margaret Cole, director of enforcement at the FSA for the past three years, said: “This sends a clear message to the UK financial services industry that it is completely unacceptable for firms to conduct business overseas without having in place appropriate anti-bribery and corruption systems and controls.”

Ms Cole told The Times on Thursday that there will be “more of the same” in 2009 and said that her 280-strong team was “very busy indeed”.

Times Recommends

• Lies and cover-up at MG Rover exposed by report
• High oil prices push manufacturing costs up
• Primark founder steps down as chief executive