Large numbers of military personnel will be used to police the London 2012 Olympics and Paralympics, deepening concerns about the final security costs for the Games.
Whitehall sources have confirmed to Sky News that advanced negotiations are under way to determine exactly how many troops will be needed to help secure the Games, but the number could top 6,000.
As yet no decision has been made as to whether the personnel will be drawn from the ranks of the territorial army, reserves, or acting military.
The shortfall in security staff came to light earlier this year when it emerged that manpower of up to 20,000 would be needed to protect the Olympic venues.
The police are also finding it difficult to fill Olympic jobs as recent cuts in the police service have left officers fearing for job security.
Previously, the London Organising Committee for the Olympic Games (LOCOG) had contracted security firm G4S to provide just 10,000 security staff, leaving organisers well short of the numbers necessary.
It is understood that financing for troop assistance will come from the overall £9.3 billion Olympic budget, rather than the overstretched resources of the Ministry of Defence.
It comes just days after the Metropolitan Police chief in charge of Olympic security, Chris Allison, admitted it is impossible to predict how much security for the Games will cost.
The security budget currently stands at £600 million, with the Government hoping for it to come in under £450 million.
However, with a contingency fund of £238 million, plus an extra £282 million allocated to LOCOG for venue-specific security, the overall spend could total more than £1.1billion.
That figure does not account for the overall counter-terrorism budget, which is central to the security of the Games, nor any additional funding for military deployment.
Elite SAS troops will reportedly form part of efforts to prevent a major security alert, such as a Mumbai-style attack, and will be stationed in boats along the Thames to allow them to respond to a situation within minutes.
The military are expected to be used for bag searches and manning airport style security gates at venues.