Aon has threatened to move its business away from syndicates that refuse to sign up to the London Market Principles 2001 (LMP2001).

A spokesman from the firm of top brokers said it “fully supports the position adopted by the London Insurance Market Brokers Committee”, which stated that brokers could take away business from underwriters that did not agree to the plans to modernise the insurance market.

Last month, chief executive Dennis Mahoney said: “We look forward to forming closer relationships with those underwriters who support the reforms that are clearly in our clients' interests.”

But now Aon, which has signed up to the plans, is openly saying LMP2001 recruits will gain more deals.

The spokesman explained business would be easier between companies using similar trading platforms and internet technology.

AON's threat comes in the light of revelations that it is drawing up contracts with Lloyd's syndicates to formalise underwriting deals.

The move is likely to lead other London Market companies to follow suit and draw up Terms of Business Agreements (TOBA), which is not the current practice.

Aon said deals it began drawing up at the end of last year, were designed to protect its interests: “The market is changing now Lloyd's has relaxed the rules of open access to brokers,” said a spokesman.