A revised work schedule allowed for the progressive handover of the stadium from next month, with the redevelopment to be substantially completed by the end of March, Multiplex officials said. But a company statement added: "There remains a material risk that these dates will not be achieved and the stadium will not be available for the FA Cup final. As previously stated, such delay, if it was to occur, would be likely to lead to significant additional costs, including liquidated damages." Industry experts predict these costs to run to hundreds of millions of dollars.

The biggest threat to the deadline is the winter weather. A prolonged spell of bad weather, which has been predicted for this winter, could derail the revised timetable. Today's statement is at odds with a statement the company made previously that the project was still on track to meet the deadline. "The Wembley situation is being fully and comprehensively addressed by the board and senior management," the statement said. "We are committed to ensuring that any further impact on shareholders is minimized as we work toward completion of this complex, problematic project."

A source in the Football Association says officials had already started making enquiries to host England's biggest sporting event, the FA Cup final, at Cardiff's Millennium Stadium if Multiplex is not ready on time. The problem is that Wembley must stage a series of test events at the stadium before Brent Council will grant a license to let football fans in.

The FA will not make a final decision on whether they switch the showpiece final to Cardiff until after the third round of the competition in January. The first round of the competition takes place this week.

Earlier this year, the admission that they had grossly underestimated the cost of building Wembley slashed Multiplex's share price and forced John Roberts to quit as executive chairman.