The announcement means the FA Cup final in May of next year is set to be played at Cardiff's Millennium Stadium for the seventh time since 2001 as wrangling over the redevelopment of Wembley continues.

"It is unlikely that the stadium will be able to stage a test event for 90,000 spectators before June 2007," Multiplex said in a statement to the Australian Stock Exchange.

Multiplex said it had advised stadium owner, Wembley National Stadiums Ltd. (WNSL), that it was entitled to a contract extension until October 2007 and was taking legal action claiming WNSL was delaying completion of the project.

The redeveloped 90,000-seater stadium in north London was originally scheduled to open early this year but the date has been successively pushed back by a series of cost overruns and disputes between Multiplex and its subcontractors.

On Monday, Michael Cunnah, WNSL's chief executive, warned that Multiplex still had "major items to complete" on the stadium.

Tuesday's announcement dashes any hopes that this month's Community Shield, the traditional curtain raiser to English Premier League season, will be held at Wembley.

Multiplex said in its statement that the stadium was largely completed, aside from the installation of some seats that were originally meant to be put in by a contractor who became insolvent.

But it said it could not achieve "practical completion" until WNSL staged test events so the stadium gained required licences and approval.

It said the stadium owner had not arranged the test events, adding to the delays.

"The problem at the moment in terms of when the stadium becomes operationally complete, or reaches practical completion, really surrounds commencement and completion of the client works," Multiplex director of communications Peter Murphy told BBC Radio 4 in Britain.

"So at this stage, Multiplex as builder is reliant upon our client, WNSL, completing a series of critical works to get us through to the point where we're capable of actually hosting or running test events and, at this stage, we're unclear and we haven't been informed by WNSL when in fact they'll commence and complete those works."

However, a spokesman for WNSL rejected the argument, saying WNSL had always stressed it could not run test events until Multiplex had finished its work. The company did not accept the new deadline, he added.

But WNSL would not confirm that the 2007 FA Cup Final would be held at Wembley.

The disagreement marks a further deterioration in the relationship between Mulitplex and WNSL, with the repeated bickering expected to be followed by a legal case in the coming month.

Multiplex cut its earnings forecasts five times last year and at last count its losses on the Wembley project were about 480 million dollars (360 milllion US).