The chief executive of G4S has said he still expects Locog to fulfil the £235m contract for Olympic security, despite the army having to step in to fill in gaps after a major blunder.

Nick Buckles' comments came in a tense evidence session with MPs, only an hour after Locog chief executive Paul Deighton said he had not paid G4S since 13 July.

So far the private security firm has been paid £90m of public money for the Olympic security contract, with the rest being "up for negotiation."

Appearing before parliament's Home Affairs Select Committee on Tuesday, CEO of G4S Nick Buckles apologised for the debacle, saying the contract was "one of a kind."

Buckles explained his company would lose an estimated £50m on the contract but it was still expecting full payment from Locog. “I expect them to pay us absolutely in line with the contract. That’s exactly that contracts are for,” he said.

But asked if he thought his company had seriously failed, and if he would step down as CEO he said "we do really need to see the results of our full review."

"When we signed the contract back in December we were absolutely sure we had to deliver on it," he said. "There's no blueprint for this [contract], there's no track record, there's no book," he said.

"I'm not going to sit here and say we did a great job. But we delivered a significant portion of that contract and our people did an excellent job and played a major part in delivering these Games. We are planning to take a £50m loss on this contract," Buckles said.

G4S told Locog they would not be able to delver on their £235m contract to provide security staff for the Olympics just two weeks before the games began.

The Home Office's head of Security Charles Farr, also giving evidence, said he would have "expected" the company to inform them of problems with the contract earlier.

"We were given sets of data which gave no indication whatever, even as late as July 1, that there was going to be a problem fulfilling that contract. That data was what G4S relied upon to explain the progress of their programme."

He said he was told on July 1 that 37,000 people had passed training, of whom 25,000 were security-screened and 21,000 accredited. The requirement was less than 15,000.

Nine thousand people were ready to work by that date, up 2,000 on two weeks before, the committee heard.

Buckles told the committee that the company was already having problems with numbers on 3 July.

But he said it was not until the firm checked the situation in detail on 10 July that staff realised they were in serious difficulties.

G4S Chief Operating officer David Taylor-Smith said the security shambles represented "a serious failure."

London 2012 chairman Sebastian Coe told the committee: "It is difficult to look beyond their inability to deliver on the contracted number of security personnel that we were consistently assured by them that they would be able to deliver."

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