The head of G4S is under pressure to quit his £830,000-a-year job as he prepares to face questions from MPs over the Olympics security debacle.
Nick Buckles, the firm's chief executive, will be asked how G4S, the world's second largest private sector employer, has failed to get enough security guards for Games venues when more than 20,000 have already been accredited.
He will face questions from Labour MP Keith Vaz, chairman of the Commons Home Affairs Select Committee, who accused his firm of letting the country down last week.
Speaking on Tuesday morning, Vaz told the BBC his committee's session was a "fact-finding mission."
Buckles, 51, would be entitled to £20 million in pay and benefits if he loses his job over the fiasco which is expected to cause his firm £50 million of losses on the high-profile contract.
More than £400 million has been wiped off the firm's value since Wednesday and Home Secretary Theresa May has been forced to appear before MPs twice in the last week over the row.
G4S repeatedly assured ministers it would "overshoot" its recruitment targets and only admitted it would fail last week, she said yesterday.
A further 3,500 troops who were drafted in to close the gap left by G4S have now been joined by officers from eight police forces after security staff failed to turn up at venues.
May said that despite more than 20,000 security staff being accredited, G4S had problems with scheduling and "getting staff to the venue security tasks".
Some staff no longer wanted the work, she added.
But May came under fire from Labour for not knowing how many staff G4S would now provide after the Home Secretary told MPs the "precise balance of the number who will be provided will become clear over the next few days".
But she denied the firm had "deliberately deceived" the Government.
A total of 3,500 troops, many of whom will be billeted at Tobacco Dock near Wapping, east London, were brought in to make up the shortfall, boosting the number of servicemen and women involved in Games security to 17,000 last week.
Hundreds of officers from eight forces have now also been drafted in to fill gaps.
Venue security was being tightened "before the full complement of accredited staff have been assigned", a G4S spokesman said.
"This situation is being rectified over the coming days, which should lead to the withdrawal of police officers from those roles assigned to private security."
The forces involved so far are Dorset, Hertfordshire, Northumbria, South Wales, Strathclyde, West Midlands, Thames Valley and Greater Manchester.
Paul Murphy, chairman of Greater Manchester Police Authority, said just 20 of the expected 58 G4S staff turned up at the main Olympic team hotel in Worsley on Saturday to help conduct a "lock-down" of the building.
Murphy told BBC Radio 4's PM: "Greater Manchester Police had to step in and ensure that the site was properly locked down.
"We have had to use officers and staff on rest days. We have had 28 Pcs and four sergeants into that area, at a cost of £30,000 a day."
The Police Federation, which represents rank-and-file officers, said the situation was "chaos, absolute chaos".
Ian Edwards, chairman of the West Midlands branch, said the force is providing 150 officers per day to cover a hotel in Warwickshire where footballers are staying.
"The worst-case scenario is that we end up having to find another 200 officers for the security at the City of Coventry stadium, and we've yet to find out what the shortfall is in Birmingham," he said.
"It's chaos, absolute chaos.
"You shouldn't lose your local police officer because of the Olympics. Communities are suffering because a private company has failed to deliver on a contract."
A confidential report by HM Inspectorate of Constabulary (HMIC) warned about concerns over security 10 months ago, leading Games organisers Locog to increase the number of security guards to be supplied by G4S from 2,000 to 10,400 while the value of the contract more than trebled from £86 million to £284 million.
She said Lord Coe, London 2012 chairman, would be writing to these staff thanking them for the job that they are doing.
"I think that to say that security is a shambles when I am out at the Olympic Village a lot of the time now, and the meticulous way in which the G4S staff, many of whom have been there for months, are screening is a testament to them," she said.
"I think that whatever failings there are, and I think there are extensive failings in the management of G4S, out on the Olympic
Park and in venues around the country there are security staff who have been through the training, who are doing the job to the very best of their ability.
"Seb Coe is writing to all the G4S staff today who have taken quite a hit over this - the management is one thing, but the staff are taking the hit - thanking them for the job that they are doing, because they are going to be very, very important over the next weeks to give us the safe, secure Games that everybody wants to be able to enjoy."
:: Reports last night suggested that US security officials will be based at UK airports including Heathrow throughout the Olympic and Paralympic period to assist American-based carriers with security issues.
Sky News reported that the Department for Transport has reached agreement with the US Transportation Security Administration for its officials to be deployed in the UK from next week and to remain until a week after the Paralympic Games end on September 9.
A DfT spokesman said: "The Department for Transport is in regular contact with the US Transportation Security Administration and we have been planning Olympics liaison arrangements with the Americans for several months.
"The department does not comment on the precise details of security matters and these arrangements have nothing whatsoever to do with G4S issue."
Shadow Olympics minister Dame Tessa Jowell told ITV's Daybreak that frontline G4S staff working on providing security had taken a "hit" for management failings.