The private firm G4S repeatedly assured ministers that they would "overshoot" their targets for recruiting Olympics security staff, the Home Secretary told the House of Commons.
Theresa May said the firm repeatedly told ministers that they would be able to recruit enough private security guards for the Games. G4S only admitted they would fall short last week, when an extra 3,500 troops were called in. Officers from nine forces will now join them to fill the shortfall.
Mrs May denied that ministers had attended G4S meetings before last week, she said:
As well as 3,500 extra troops, police officers from Dorset, Surrey, Hertfordshire, Northumbria, South Wales, Strathclyde, West Midlands, Thames Valley Police and Greater Manchester Police have now been drafted in to close the gap.
G4S, which has seen its shares dive by as much as 10% following the Games security debacle, said venue security was being tightened "before the full complement of accredited staff have been assigned".
The Home Secretary told MPs during an urgent question that G4Shave more than 20,000 accredited Olympics security staff but the issue was scheduling and "getting staff to the venue security tasks".
Mrs May denied G4S had "deliberately deceived" the government, telling MPs that the firm made clear that the problem with "workforce supply and scheduling" only emerged "over the last couple of weeks".
Shadow Home Secretary Yvette Cooper earlier questioned the competence of Mrs May over the security debacle.
With less than two weeks until the opening ceremony, ministers insisted the Games would be secure. Hundreds of police officers are now being deployed along with the 3,500 servicemen and women who were called in last week.
West Midlands Police Federation chairman Ian Edwards said it was "chaos, absolute chaos", with his force having to provide 150 officers per day to cover a hotel where footballers are staying, he said:
Clive Chamberlain, chairman of Dorset Police Federation, said G4S staff were simply not turning up.
ITV News reported in May there were serious concerns about G4S's ability to provide enough trained staff. A letter from the company to our UK Editor seemed to confirm that managers were aware of delays on recruitment months ago.
David Cameron said the government had been monitoring potential Olympic problems since it took power and Deputy Prime Minister Nick Clegg predicted that London would "deliver a secure" Games.
G4S chief executive Nick Buckles - who is due before the Commons Home Affairs Committee tomorrow - has admitted he may be forced to quit his £830,000-a-year job in the wake of the Olympics debacle.
The FTSE 100 Index firm has admitted that it will incur a loss of up to £50 million on the high-profile contract.