Britain's stretched border service is letting terrorist suspects slip into the country, a newspaper has reported, quoting two unnamed Border Agency officials as saying several suspects have been waved through controls at London's Heathrow Airport since the beginning of the month.The Observer newspaper's report - which Britain's Home Office declined to comment on - is the latest in a series of last-minute concerns to surface as London gets ready to host the 2012 Olympic Games.Officials are already under pressure over the failure of security contractor G4S to deliver some 10,400 personnel to protect stadiums and other events.The blunder has forced the government to call in an extra 3500 troops to guard the Games - that's over and above the 7500 troops already promised to help out at some 100 venues and sensitive sites.Blame has started to fly, with the Observer saying immigration staff had missed several members of a security watch list whose arrival in the country was meant to have been reported to counter-terrorism police or Britain's domestic intelligence service.The newspaper cited unions as suggesting that staff brought in to help relieve the 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 during peak times, leading to fears of Olympics-related chaos as tourists fly in to watch the Games.Meanwhile The Independent on Sunday newspaper reported that top Home Office officials had been warned by police nearly a year ago about the inability of G4S to provide enough staff, while the BBC quoted the chief of Britain's National Association of Retired Police Officers as saying his group could have helped fill the shortfall in manpower - if only G4S had bothered getting in touch.The minister in charge of the Olympics appeared on a Sunday morning TV talk show to try to calm the uproar."I don't think this is a moment for getting into the blame game actually," Hunt told the BBC."G4S has been quite honorable. They put their hands up. Nick Buckles, their chief executive, has said they got it wrong. They've apologised. They're going to cover all the costs."