The new Wembley Stadium will have a 90,000 capacity

Martin Tidd, Multiplex's UK managing director, said there was a 70% chance the stadium would be ready.

Tidd said Multiplex could not afford any further delays if it was to meet the 31 March deadline to hand the �757m project to the Football Association.

But BBC Sport understands the FA doubts whether Wembley will be ready in time.

FA books Cardiff as final back-up

The FA has provisionally booked Cardiff's Millennium Stadium for the FA Cup final as a contingency plan.

Tidd said Multiplex would know in two or three weeks whether it would be in a position to complete the stadium by 31 March, but that it needed everything to go "like a Swiss watch".

We have 3,500 guys putting huge pressure on the contractors to drive the job over the line Multiplex UK managing director Martin Tidd

Michael Cunnah, chief executive of Wembley National Stadium limited, said his company would be working closely with Multiplex.

"We will continue to monitor progress on a daily basis and take their expert advice on how the stadium is progressing," said Cunnah.

The main obstacle to completing the stadium on time is the "depropping" of the roof on the south side of the stadium.

In layman's terms, this means taking the supporting structures - steel cables and so on - away to allow the roof to ease into its final position.

But this work will be at the mercy of the weather; winds stronger than seven knots would mean that the roof could not be safely worked on.

Who secretly hopes Wembley won't be ready in time for the FA Cup final? From RK Have your say on 606

Tidd said the work would also depend on the performance of subcontractors, design changes and relations with trade unions.

"It does not all come down to us at the end of the day - there's a lot of people needed to make sure the FA Cup comes off," he said.

WEMBLEY FACTS & FIGURES Of 90,000 seats, 45,000 are in place Of 161 hospitality boxes, 24 are "substantially complete" Of 127 toilet pods, eight are complete Of 44 catering kiosks, four are complete

"We have 3,500 guys putting huge pressure on the contractors to drive the job over the line.

"There's still a risk and we are managing it, but there may be other contractors out there that might not see it through."

Earlier on Monday a Multiplex spokesman had said Wembley was still on target to hand the project over to Wembley National Stadium Ltd, the company set up by the FA to run the stadium.

Multiplex has issued four profits warnings since last August.

Difficulties with the redevelopment of the 90,000-seat stadium prompted the resignation of Multiplex executive chairman John Roberts in May as the group blamed "cost blow-outs" for the spiralling cost of the stadium.

New Wembley costs to rise by �75m