The fall-out from the Spitzer inquiry in the US has led to concerns that Marsh could "unwind as quickly as Andersen", according to a leading insurance analyst.
Accountant Mazars said it was the major UK brokers, rather than the mid-tier players, that were at greater risk, as they tended to use placement service agreements (PSAs).
A Mazars spokesman said: "The problem lies with larger brokers - they have the financial clout to move accounts around and come up with these deals. As far as we can glean, it's pretty widespread.
"[The Spitzer inquiry] will improve disclosure and it will force more companies to look at reputational risk. People are already asking if Marsh could unwind as quickly as [accounting firm] Andersen."
PSAs are deals between brokers and underwriters whereby brokers receive extra fees in exchange for producing premium volumes to underwriters.
It is understood that Marsh and Aon charged on average 2.5% as a broker commission on volume business.
Following New York attorney general Eliot Spitzer's decision to sue Marsh for fraud and violation of US competition regulations as a result of the broker's use of PSAs, GISC has called on anyone with concerns about the use of PSAs in the UK to alert it.
"We would investigate any specific complaint, but there has been a lack of people coming forward. If people are concerned they should come forward," said GISC.
One chief executive of a US insurer with a branch office in London said PSAs were common in the UK market. "It's not solely a US problem, most of the PSAs we have are with brokers in London," he said.
Meanwhile, one chief executive of a leading Lloyd's managing agent called for PSAs to be scrapped in the UK. "I'd like to see an end to them because there should be more transparency," he said.
An FSA spokesman said its rules on inducements would mean that PSAs would be banned from 14 January 2005 when FSA regulation comes into effect.
Spitzer has also subpoened Aon and Willis and his suit names AIG, Chubb, Ace, Hartford and Munich American Risk Partners as participating in giving Marsh illegal kick-backs.
Though charges against Aon have not been filed, its share price has fallen from $27.78 last Tuesday to $19.35 at 12pm on 19 October.