Private security firm G4S repeatedly told ministers that it would "overshoot" its targets for recruiting security guards for the Olympics, Theresa May has said.
The home secretary told MPs on Monday that G4S only told the government that they would be unable to meet their contractual arrangements last Wednesday.
"G4S repeatedly assured us they were going to overshoot their target not undershoot it," May said.
However she said G4S had not "deliberately deceived" the government as the company itself had only discovered it had a problem "over the last couple of weeks".
And she dismissed as "untrue" allegations that ministers had known about the shortfall as long ago as 2011.
The government has been forced to draft in an extra 3,500 troops and officers from nine police forces to provide security for the games after G4S admitted it would be unable to fulfil its contract.
The recriminations over G4S' handling over Olympic security as the first Olympic athletes arrived at Heathrow on Monday, with the airport expecting to handle a record number of passengers.
A total of 335 athletes are expected today as well as 236,955 passengers, breaking the previous record of 233,562 set on 31 July 2011.
Three-hundred and thirty-five Olympians from more than 50 countries, with family members, are set to pass through the airport on Monday, with the US sailing team among the first to arrive.