Home Secretary Theresa May has told MPs that the security operation for the 2012 Olympic Games had been "meticulously planned" and would not be compromised, following the revelation that that 3,500 extra troops would be needed.
Mrs May was responding to an urgent question on Olympic Games security on 12 July 2012, tabled by the Labour MP and chairman of the Home Affairs Committee, Keith Vaz.
The government is drafting 3,500 extra troops in for Olympics security, in addition to 13,500 already agreed, amid fears contractor G4S may not have enough trained staff.
The home secretary said the security operation for the games was the largest and most complex since World War II and that contingency plans were a central part.
"We built in flexibility to respond to any challenge," she said.
Mr May said ministers "recognise the burden" on servicemen and women and they would receive full leave entitlement, and 10,000 Olympic and Paralympic tickets would be donated to the armed services.
She emphasised there was "no specific security threat and the threat level remains unchanged".
Security firm G4S said it had "encountered some delays" in processing applicants through the final stages of training.
Keith Vaz endorsed the decision to provide additional troops but claimed that the London Organising Committee of the Olympic Games (Locog) knew of concerns about a shortfall of security personnel two weeks ago, and asked when ministers became aware.
He also asked if G4S would face penalties over what he called a "fiasco".
"G4S has let the country down and we have literally had to send in the troops," he said.
Mr May insisted the government only found out on Wednesday that G4S had a lack of trained staff.
Shadow home secretary Yvette Cooper gave Labour's support for the extra deployment of troops under the circumstances but said: "This looks like another Home Office shambles."
The home secretary said the government was taking the action necessary and that troops were always part of the contingency plans.
G4S is being paid £300m to supply 10,000 guards for the Games, but the BBC understands it has not been able to guarantee it can deliver that number.