Eliot Spitzer's investigation is forcing changes in the industry

The five who stepped down all worked for the firm, which was criticised for having too many insiders on the board.

Marsh is at the centre of allegations by New York attorney-general Eliot Spitzer that insurance firms and brokers fixed bids for corporate cover.

Separately, California is now suing four insurers on similar allegations.

The state's insurance commissioner, John Garamendi, started his investigation of alleged kickbacks in exchange for big contracts in October.

He has now started action against four firms - MetLife, Prudential Financial, Cigna and UnumProvident.

A fifth, Universal Life, is not being charged, said Mr Garamendi, in exchange for "full and timely" co-operation in investigating the other four.

Insiders

But the main show remains in New York, where Mr Spitzer is continuing to expand his probe.

He testified earlier this week to Congress about the investigation, saying the action to date represented only "the tip of the iceberg".

He has already collected the scalp of Marsh's former chief executive, Jeff Greenberg.

His successor, Michael Cherkaskey, is now the only insider on Marsh & McLennan's 11-person board.

"Marsh's action is a very significant step in implementing the kind of management that the public and shareholders have been wanting since the collapse of Enron," said Larry Soderquist, who heads the Corporate and Securities Law Institute at Nashville's Vanderbilt University.

Marsh has agreed to change its practices to avoid a repeat of the kickbacks. It is also planning to cut 3,000 jobs.