Multiplex is attempting to force Cleveland Bridge to reveal documents it believes are held in Saudi Arabia by one of its parent company's directors amid claims the steel firm is holding vital information on Wembley.

Multiplex believes that a search of offices in Saudi Arabia may uncover evidence of a plan, codenamed Project Trafalgar, for the steelwork contractor to stop work on the pretext that Multiplex had breached the terms of its contract.

The allegation has sparked a fresh row in the £50m legal battle between the two parties, which is scheduled to go to court next month.

In January, Multiplex joined Dorman Long Engineering, Cleveland Bridge's parent company, to the court action, alleging that it had breached its parent company guarantee.

Building has learned that Cleveland Bridge's lawyers have written to Multiplex saying a search of an office used by a director of Dorman Long Engineering would not be "reasonable and proportionate".

Multiplex has reserved the right to make an application in court to force Cleveland Bridge to conduct the search.

A Multiplex source said: "We want to find out what instructions it gave down the line and what information it has concerning Wembley and Cleveland Bridge's approach to the project."

Multiplex has reduced its defects claims against Cleveland Bridge from £5.6m to £3.9m. The biggest reduction is over the claim relating to the design and materials of the roof. The defects claims will be heard in a trial to be held next year.