A source at the site said Multiplex, the contractor in charge of the project, had called in the police to check areas where a bomb could be concealed while they could still be inspected. The source said: "The police have been checking voids and ducts on pipe works before they are sealed to make sure there are no explosives or anything that shouldn't be in there."
The source added that the measure had been taken because Wembley's high profile made it a potential terrorist target.
The source said: "The stadium is always going to have tight security measures and it is felt that this must begin at the construction phase."
A spokesperson for Multiplex confirmed the company was working with the police. She said: "Multiplex did have a meeting with police recently concerning the inspection of voids, and this is a standard procedure, especially on high-profile projects such as Wembley."
However, one leading contractor said that calling in the police to inspect the project was an unusual step. He said: "Internal company teams would normally sign off parts of projects on risky schemes such as prisons, but this would normally be carried out by industry figures and not the police."
In an interview with Building last September, leading terrorism expert Georg Sieber warned that terrorists could be planting bombs on sites. Munich-based psychologist Sieber, who predicted the murder of 11 Israeli athletes at the 1972 Olympics, said that terrorists could exploit poor security to place radio-activated bombs inside half-finished buildings with a view to detonating them months or even years later.
The Metropolitan Police have a permanent station on the Wembley site, although it is understood that it is not permanently manned.