A consortium of London insurers, including Equitas and CGNU, has had the potential payout for a flood in Chicago in 1992 cut from $141m (£97m) to $41m (£28m), following a ruling by the US Court of Appeal.
The insurers covered the Great Lakes Dredge & Dock Company, which was found responsible for the collapse of a tunnel which led to extensive flood damage in the city.
The company had been doing piling work in the Chicago River and was found to have weakened the tunnel.
The court ruled that the group of London insurers only had to pay out on policies in place at the time of the flood.
Great Lakes had been trying to recover money from policies in force in 1991, when the initial damage to the tunnel was thought to have happened.