Willis has started an "aggressive" marketing drive to grab new clients from rivals in the past few weeks

In a letter to clients, dated 16 November, Willis chairman and chief executive Joe Plumeri outlined the broker's approach to the market and the need for "a trusted partner".

He said the broker had made "practical" decisions to do "what is best for the client" particularly back in 2001 when the broker rejected an offer from a group of investors to establish an insurer.

Plumeri said: "We passed on the opportunity because we believe that when brokers have an ownership stake in insurers there is a potential conflict of interest.

"Brokers who have invested in insurers are now being asked to explain their decisions - this is not an issue for us."

He added: "We sold off any hobby (sic) businesses - there are no distractions."

Willis regards itself as a "one flag company" and tackles the business through its "Glocal approach", (an amalgam of 'global' and 'local'), highlighting its emphasis on UK regional brokers through the Willis Commercial Network.

A Willis spokesman said: "We said on 27 October, when our results were published, that we would be aggressively targeting new clients and looking to hire new producers. Joe's letter is part of the drive."

Concrete manufacturer RMC Group global risk and insurance executive Richard Storey, who at present is a Marsh client, said: "I have received a letter from Willis outlining its strategy and also a letter in recent weeks from the local Willis broker asking me if I am happy with my broker.

"The letters seem to have appeared since the Spitzer inquiry began," he added.