Crowe Syndicate Management is selling its two operating syndicates.
The decision comes following the failure of a management buy-out (MBO).
Earlier this year, managing director Richard Murphy headed up a team to purchase the Lloyd's managing agent.
But its new main capital supporter has indicated it is only willing to provide funding for a year following the World Trade Centre tragedy.
It said it wanted to reserve its capital for investment in the international specialty reinsurance markets instead.
The board has now rejected the MBO's short-term financial offer and is selling UK motor syndicate 963 and life syndicate 982.
A third-party purchaser has been offered exclusive talks over the sale of syndicate 963.
A Crowe spokesman said the London run-off syndicates (53, 808, 1121 and 1204) would remain with Crowe Syndicate Management for the time being.