The head of security firm Group Four Security (G4S), the private contractor charged with securing London's Olympic facilities, told the BBC he does not know how many of its 10,000 security guards are able to speak English.

Beleaguered security boss Nick Buckles has come under intense scrutiny after it emerged earlier this week that G4S had failed to recruit enough guards, leaving the UK Government to make up the shortfall with soldiers -- many of whom are thought to be on Summer leave -- and extra police units.

Speaking to BBC Radio 4's Today program, Buckles could neither confirm or deny allegations G4S had been so rushed to recruit the required number of guards it had neglected to check if recruits had a basic command of the English language.

That is a difficult question to answer. They all have a right to work in the UK and have been vetted to very high standards, he said in response to the allegation.

When asked again how many could speak English, he added: I can't say categorically.

Earlier this week, Buckles said that his firm only realized just over a week ago it would not be able to supply enough venue guards for this month's London Olympics, as he publicly apologized for the embarrassing failure.

The news came as G4S said it would incur a loss of up to £50 million ($77.7 million) for the problem, which has forced the British government to put 3,500 extra troops on standby to fill the gap.

Speaking to BBC News, Buckles said the FTSE 100-listed company, whose shares fell in the past 24 hours to their lowest level for almost a month, realized there would be a shortfall only eight or nine days ago.

Clearly we aren't going to deliver on our element [of the security operation], and we're very, very disappointed about that and embarrassed, he said.

He said at the moment they had 4,000 trained guards in place with another 9,000 in the pipeline.

The failure has dominated news headlines in Britain with the games starting in less than two weeks, on July 27, and many of those recruited by G4S have contacted the media to say the recruitment and training process had been a shambles.

They have been hiding behind a 'need-to-know basis' and saying they do not want to tell people what is happening because it is a security threat, a would-be G4S employee, who has had two weeks' training on X-ray scanning equipment, told Reuters.

But, in essence, they just do not know.