The stadium arch is more than 400ft tall

The move follows Darlington-based Cleveland Bridge's failure to reach an agreement on the transfer of staff. The company supplied a huge steel arch costing �60m, which is the centrepiece of the new ground.

Cleveland Bridge and main contractor Multiplex issued statements saying the Darlington firm would be quitting the project in a matter of weeks.

Cleveland Bridge was unable to come to a deal over its contract staff with Dutch-based Hollandia, who is taking responsibility for the on-site steel erection.

Cleveland Bridge worked on the design, manufacture and installation of the Wembley Arch, which was lifted into place last week, and was contracted to work on the stadium bowl and roof.

The new stadium will open in 2006

No reasons have been given for the departure of Cleveland Bridge from the project.

A statement from Australia-based Multiplex said Cleveland Bridge would continue to be actively involved in design, fabrication and delivery of steel.

A Cleveland Bridge spokesman said: "We have successfully completed the most challenging part of the Wembley stadium job, assisting on the technical design, its construction and the lifting of the Wembley Arch.

"The Arch will stand not only as a geographical landmark but also testament to the ground-breaking achievement of Cleveland Bridge and all of the staff who collaborated on the project."

The 1,800-tonne arch, which has a span of 315m, can be seen across London.

The raising of the arch was delayed in March after tests showed weak spots.

Computer tests found welding faults and problems with the concrete foundations.

Multiplex Construction UK, the contractor for the Wembley Stadium project, said the defects were discovered during "quality assurance checks".

The stadium is due to open in 2006.

The 2006 FA Cup Final is set to be the stadium's first match.