Armed forces on Olympics standby
11 July 2012 Last updated at 22:43 BST
The BBC has learned that the Army is to provide up to 3,500 troops to help with Olympic security.
The move comes amid fears that the private contractor G4S would not be able to provide enough trained staff in time.
The armed forces are already providing some 13,500 personnel.
This could now reach 17,000, meaning summer leave for some troops will likely be cancelled.
The BBC's Defence correspondent Caroline Wyatt reports.