South side of stadium is believed to have sunk 16 mm - although Multiplex insists no subsidence has taken place.
Concrete contractor PC Harrington is carrying out work to tackle subsidence at Wembley stadium, it emerged this week.
The firm, which is already carrying out remedial works on the sewerage system, is thought to have been asked to expand its role.
Multiplex has strenuously denied reports that the stadium is sinking after the Conservative party called for assurances on the issue on Monday. A Multiplex spokesperson said: "There is absolutely no truth to reports that Wembley stadium is subsiding. We utterly reject these claims." Yet Building understands that the south side of the stadium has suffered subsidence of 16 mm.
The Multiplex spokesperson conceded that on a project the scale of Wembley, there were "bound to be a number of snagging issues". PC Harrington was unavailable for comment.
A last minute deal between Multiplex, steel contractor Hollandia, and Fast Track, a labour agency, has averted a dispute in which the steel workforce would have been withdrawn. Multiplex had offered to employ the workers directly but did not have to as a payment problem involving Hollandia and Fast Track was resolved.
Building understands that at least two other subcontractors on the project have held talks with Multiplex over payment this week. The subcontractors are understood to have demanded assurances over payment before carrying out the final stages of their work, amid growing concern over Multiplex's financial loss on the scheme.
Meanwhile, it has emerged that Wembley contractor Multiplex is receiving legal advice on a potential claim against Wembley National Stadium Limited after claiming it ought not to face financial penalties for delays on the project.
Legal firm Clifford Chance is understood to be advising Multiplex on a potential case against WNSL after the firm said it was entitled to finish the project until September without facing penalties because of design changes allegedly introduced by the client.
A Multiplex source said the firm was receiving legal advice from Clifford Chance in an attempt to avoid paying £120,000-a-day fines for the late completion of the stadium, which it now claims will be finished in June.
In a further sign of approaching litigation it emerged this week that Multiplex had hired dispute resolution specialist Fenwick Elliot to fight a growing number of claims from subcontractors.
However, FA chief executive Michael Cunnah has said he believes the delays are "100% the fault of Multiplex", and senior football sources have told Building that no design changes were made to the main steel structure of the stadium.