Multiplex chief executive Andrew Roberts said: 'The Wembley result is unacceptable and completely overshadows the strong results from all other parts of the business.'
Including the £20 million indemnity against Wembley losses already put up by the Roberts family, the firm is facing losses totalling £45 million.
But even achieving this disastrous result is dependent on winning claims against third parties, its ability to meet the project's schedule and costs involved with finishing Wembley's steelwork.
The sum could eventually exceed the £60 million reverse that the former Laing Construction took on the Cardiff Millennium Stadium.
Multiplex said that it had undertaken a review of the scheme since February and drafted in new management.
And the company admitted that it would not be able to hand over Wembley until March 2006 - just in time for next year's FA Cup final.