Lloyd's marine underwriters fear that the new franchise performance board will "come down on them like a tonne of bricks".
This was the response to a speech made by Lloyd's new franchise performance director Rolf Tolle on Tuesday in which he warned underwriters that they will be forced to write only profitable lines of business.
One marine underwriter said: "The marine market has not fully appreciated the impact of the franchise board.
"Once the board gets to work it will come down like a tonne of bricks on marine underwriters. But that is a good thing - it will take the bad underwriters out of the market."
The marine market has not made a profit since 1996.
Speaking at a lecture in the Lloyd's Old Library on Tuesday, he said that the profitability of the market had been compromised by the "virus of top line gross", causing underwriters to focus on top line rather than bottom line profits.
"The market needs to ask itself whether there were any lines of business that should be rejected by Lloyds," he said.
"Lloyd's should not be writing any lines of business that can only be profitable through investment income."
Improving bottom line profits was essential if Lloyd's was to improve its security rating from
A minus to A, Tolle said.
He also added that the franchise board would monitor syndicates' performance and use its powers to influence which classes of business capital were being promoted.
And he gave a warning to all syndicates that he would not fail to use his powers of enforcement if necessary: "The powers are there and will be used."
Reactions to his comments were mixed. Chaucer managing director Ewen Gilmour was cautiously optimistic. "If we have to have a little restriction on what we write to avoid the profitable syndicates paying for the losses of the unprofitable ones then we are right behind him. The problem will come if it restricts our scope too much - then it will not work."
Ascot active underwriter Martin Reith was concerned that problems might arise if the franchise board took a different view to syndicates as to what was profitable: "An underwriter may take a long-term view on the profitability of a particular market, that the board may disagree with."
Market sources have also raised concerns that Tolle may focus on smaller players because larger corporates now have too much power.