London 2012: May defends Games security plans
Contractor G4S "repeatedly assured" ministers they would "overshoot their targets" for Olympics security staffing, Theresa May has told MPs.
Addressing the Commons, the home secretary also denied allegations the government knew before Wednesday there would not be enough guards.
Labour said it was "incomprehensible" Mrs May had not known earlier.
It comes after G4S admitted it would fall short last week, with 3,500 extra troops now being deployed for security.
Meanwhile, it has also emerged that police have had to deploy extra officers from eight UK forces to do Olympic security work.
Mrs May was answering an urgent question from Yvette Cooper MP, the shadow home secretary, on "security arrangements for the Olympic Games in light of the inability of G4S to deliver its contract".
During the day athletes and officials have been arriving at the Olympic Village with Heathrow Airport experiencing its busiest day on record, and the first priority "Games Lane" in operation.
Speaking to BBC Newsnight, Culture Secretary Jeremy Hunt said it was not time for a "witch hunt" against G4S.
"What we actually want is for G4S to deliver on what they say they can deliver."
In her statement to MPs, Mrs May insisted the government had reacted quickly when it discovered G4S was in difficulty.
"G4S only told the government that they would be unable to meet their contractual arrangements last Wednesday and we took immediate action," she said.
She also denied G4S had "deliberately deceived" the government, insisting the firm's problem was "workforce supply and scheduling".
Mrs May did not confirm how many staff G4S would now provide, but added the government was "on course to deliver a safe and secure Games that everybody will enjoy".
But Labour's Yvette Cooper said Mrs May should have known about the problem.
"Even G4S say they have been discussing the detailed shortfall for eight or nine days, yet last Monday the home secretary told the House she was confident our partners will deliver.
"It is incomprehensible that monitoring was that poor that no one told her until Wednesday," she said.
"How on earth could the minister responsible for delivering Olympic security be the only person who didn't know?"
Ms Cooper also told MPs Tory London Mayor Boris Johnson had admitted the problems were known about "ages ago", and his deputy Stephen Greenhalgh had claimed security concerns had been raised "repeatedly".
G4S, whose shares have fallen by 9% since the problems arose, said security was being tightened at venues before "the full complement of accredited staff have been assigned".
It said: "Some venues are being supported by police in the short term, while the private security workforce is being mobilised.
"This situation is being rectified over the coming days, which should lead to the withdrawal of police from those roles assigned to private security."
Earlier, Manchester police had to deploy officers to provide security at a hotel in Salford where four Olympic football teams will stay - after only 17 of an expected 56 G4S staff turned up for work.
Police said there had been no failure to provide security for athletes.
But Paul Murphy, chairman of Greater Manchester Police Authority told the BBC using staff on rest days had cost the force £30,000 a day.
The prime minister's official spokesman refused to be drawn on when David Cameron was aware of G4S's Olympic recruitment failings, but said he was involved in the decision to deploy extra soldiers.
On the issue of the cost of the unscheduled call-up to the armed forces, the prime minister's spokesman said: "We are very keen to make sure absolutely no one loses out.
"G4S have been clear they will meet the costs."
Mrs May told the Commons last week that there were penalties written into the G4S contract but did not give details.
Late on Friday, G4S said it faced a £35m-£50m loss on the £284m contract after failing to recruit enough security guards for the Olympics.
There is now speculation that G4S chief executive Nick Buckles - who is due to appear before the Commons Home Affairs Select Committee on Tuesday - could lose his job, after chairman John Connolly hinted that senior heads could roll.
Mr Buckles admitted he was "bitterly disappointed" at his company's failure to meet the terms of the contract.