Olympics security will not be compromised, Home Secretary Theresa May has said, after it emerged 3,500 extra troops would be needed.
She said it was only discovered on Wednesday - 16 days before the Games begin - that contractor G4S did not have enough trained security staff.
The troops are in addition to 7,500 already agreed for venue security.
Labour MP Keith Vaz said: "G4S has let the country down and we have literally had to send in the troops."
G4S was contracted by the London 2012 Organising Committee to supply 13,000 staff.
It said it had 4,000 people already working across 100 venues, with a further 9,000 going through the final stages of extensive training, vetting and accreditation.
"We have encountered some delays in progressing applicants through the final stages but we are working extremely hard to process these as swiftly as possible," the company said.
Mrs May addressed the Commons in response to an urgent question from Mr Vaz.
"Can the home secretary give the House this assurance: that she is now satisfied that all the changes she's announced today will mean that this, what we hope will be the greatest Games ever staged, will be done securely for the safety of the visitors and the British people?," he said.
'Most important' task
Mrs May responded: "I can confirm to the House that there remains no specific security threat to the Games and the threat level remains unchanged.
"And let me reiterate that there is no question of Olympic security being compromised."
Mrs May said Britain had the "finest military personnel in the world".
Source: BBC News