Britain's interior minister says the security firm G4S repeatedly assured the government it would exceed its targets for recruiting Olympic staff and only admitted last week it could not meet the terms of its contract.

Home Secretary Theresa May said Monday that G4S had "repeatedly assured us that they would overshoot their target."

Britain is calling in 3,500 extra troops to cover the positions G4S could not fill.

G4S chairman John Connolly says senior managers could lose their jobs over the fiasco.

The company said Monday its loss on the contract would range between $54 million and $78 million US in this financial year.

A loss of $78 million is about 12 to 13 per cent of the company's annual profit, analysts calculated.

The country's Olympic security plans fell under fresh scrutiny Sunday, with a newspaper report that several people on a terrorism watch list have been waved through airport border controls without being flagged and the revelation that the government was warned 10 months ago about the ability of G4S to fulfil its staffing obligations.

With less than two weeks until the opening ceremony, and athletes from around the world starting to arrive for the Games, government ministers are insisting the Games will be secure and dismissing the G4S fiasco as no more than a "hitch."

'It is incomprehensible that the Home Office didn't know about this.'— Labour Party MP Yvette Cooper

However, those assurances are being increasingly questioned. The Observer reported Sunday that, since the start of the month, immigration staff at London's Heathrow Airport have let through several people on a security watch list. When people on the list arrive in the country, it is supposed to be reported to counter-terrorism police or Britain's domestic intelligence service.

The newspaper cited unions as suggesting staff brought in to help relieve pressure at Heathrow, which has faced recurring problems handling large influxes of passengers, weren't being properly trained. The airport, Europe's busiest, has recently struggled to clear huge lines that build up at immigration checkpoints during peak times, leading to fears of Olympics-related chaos as tourists fly in to watch the games.

London has four other airports, but Heathrow is the only airport where participants can get their Olympic credentials, so it is handling the bulk of arrivals for the Olympics, which start July 27 and end Aug. 12.

The newspaper report left it unclear whether the people on the watch list were still in the country, whether they were intercepted later, or exactly why they had attracted the attention of counter-terrorism officials in the first place. Britain's Home Office declined to comment Sunday on the story.

G4S warning issued 10 months ago

In another development, the Independent on Sunday newspaper reported top Home Office officials had been warned by police nearly a year ago about concerns over the ability of G4S to provide enough staff for the Olympics. The warning came last September in a report by Her Majesty's Inspectorate of Constabulary, the national police oversight body.

Some action was taken in the wake of that report, namely increasing to 10,400 from 2,000 the number of security guards requested from G4S. However, the firm confirmed last week it will be unable to supply the needed staff, which will require at least 3,500 additional British troops to be deployed instead — all at G4S's cost.

The British minister in charge of the Olympics appeared on a BBC talk show Sunday to try to contain the scandal. Jeremy Hunt noted that G4S boss Nick Buckles had apologized and would be footing the bill for the last-minute military deployment. Buckles, who is due before a House of Commons committee Tuesday, has admitted he may be forced to quit his $1.3-million-a-year job in the wake of the Olympic debacle.

"I don't think this is a moment for getting into the blame game," Hunt said. "G4S has been quite honourable. They put their hands up. Nick Buckles, their chief executive, has said they got it wrong."

Hunt insisted the government realized only last week that G4S would not be able to meet its targets and that it immediately activated its contingency plans.

Yvette Cooper, the opposition Labour Party's critic for the Home Office, blasted the government for their handling of the situation.

"It is incomprehensible that the Home Office didn't know about this," she said.