Theresa May has insisted she is 'getting a grip' on the Olympic security row after being told it is "incomprehensible" she was unaware of problems at G4S before last week.
The home secretary told MPs after being summoned to the Commons for an emergency debate that she had first heard of contractor G4S' failure to recruit 10,400 security guards at Olympic venues last Wednesday.
Parliamentarians repeatedly suggested either that G4S deliberately deceived ministers as to their progress on the target or that May was incompetent. The home secretary said G4S had said it looked like overshooting the security staff target before abruptly admitting the problem last week.
Last Wednesday the government called up an extra 3,500 military personnel for Olympic security duty, after G4S admitted it was struggling to recruit enough guards.
May's position, greeted with incredulity by opposition politicians last week, was called further into question by a series of media reports over the weekend.
Officials at the Ministry of Defence put 4,000 military personnel on standby in April because of concerns over the ability of private guards to do the job, the Times newspaper reported.
That followed yesterday's revelation in the Independent on Sunday newspaper that May had been warned by Her Majesty's Inspectorate of Constabulary in September that G4S may not be able to provide enough guards.
Shadow home secretary Yvette Cooper told MPs this afternoon: "It is incomprehensible that monitoring was that poor that no one told her till Wednesday... we need to know why the home secretary has failed on this."
She pointed out that a Manchester venue's lockdown had failed because of a shortage in staff caused by G4S and that local police officers had to stand in.
May denied that ministers knew of the shortfall in security staff before last week, however. She said the Home Office had monitored security plans carefully.
"G4S did not deceive the government - they assured the government they could deliver the [staff]," she told MPs, amid intense laughter from the opposition backbenches.
G4S' chief executive Nick Buckles will appear before the home affairs committee tomorrow to answer questions.
He has claimed he only knew that problems were emerging within the last two weeks.
Labour has called for G4S to pay for its errors by paying for an 'Olympic bonus' for British troops, along the lines of those already awarded to bus drivers and tube drivers.
"Many are cancelling well-earned summer leave with their families to cover for G4S and ministers' mistakes," shadow armed forces minister Kevan Jones said on Sunday.
"Ministers need to make sure they get a bonus in recognition of their contribution."
G4S' failure is being seized on by critics of the government's enthusiasm for the private sector.
With preparations for the Games proceeding smoothly, newspapers have focused on security issues as an area of particular controversy.
The decision to site anti-air missiles in residential locations around the Olympic Park had triggered a legal challenge which was subsequently defeated.
"Most people living in London will be hugely reassured by the presence of our armed forces," defence secretary Philip Hammond told MPs.