The London market is bracing itself for huge losses from US casualty business, which could be worse than those caused by the 11 September terrorist attacks.

A senior market source said actuaries believed 15 separate losses, each totalling at least $1bn, would soon be hitting Lloyd's and the London market, as a result of the fall-out from the collapse of Enron, WorldCom and other corporate disasters.

The claims would hit underwriters with large books of US directors' and officers' insurance hardest as multi-million dollar lawsuits land on policyholders' desks.

"US casualty is about to get clobbered and this will be worse than WTC," the source said. "It's taken them this long to figure out who to sue."

The lag between high-profile corporate collapses and claims against insurers reflects the time taken by lawyers to identify the problems that caused failure and settle on a strategy.

The source said that Lloyd's syndicates with outstanding US casualty books would soon start to suffer, and the warning came as XL warned that US casualty losses would hit its third quarter results.

The Bermuda-based company said new claims had surfaced for the 1997 to 2000 underwriting years cutting $184m pre-tax off the quarter's income.

XL is due to announce its third quarter results on 29 October.