The consortium of insurers who covered the World Trade Centre in New York has completed their case on why they shouldn’t pay leaseholder Larry Silverstein twice for the September 11 attacks.

But the final witness, Willis broker Nicholas Dunlop, admitted he thought the cover was to be organised using a standard Travelers Insurance form rather than the “Wilprop” form the insurers insist they were using. But he also admitted he didn’t tell the insurers.

The Wilprop form says the insurers were placing cover against a single event, and that the attacks on the twin towers were one event. The Travelers form is rather more flexible, and contains no definition of “event”. At stake is half the $7.1 billion Mr Silverstein is claiming.

What makes it important is that Mr Silverstein has already lost his case against the Wilprop form, but still insists the insurers – led by Swiss Re – knew he was in the process of switching to the Travelers form. The insurers deny this.

Judge Michael Mukasey will begin instructing the jury next week, with a verdict expected a few days later.