Lloyd's insurer SVB increased its loss estimate from the World Trade Centre attacks in the US from £20m to £30m.
The new figure is equivalent to a loss of about 15p a share before tax. Its original estimate, made on 17 September, was just over 10p per share.
The company, which operates five syndicates on the Lloyd's market, said the increase was a result of new notifications of claims and revisions of previous notifications.
The estimate includes provision for reinsurance payments and bad debt.
SVB last month bought £30.4m of extra capacity at Lloyd's, which it said would increase its opportunity to profit from rising rates.
