BBC Security Correspondent Gordon Corera talks to the people behind the largest security operation in peacetime, designed to ensure the Olympic Games go ahead without interruption.
This is the first time the games have been held in a 'high threat' environment, presenting unprecedented challenges to the police and intelligence services. The cost of security is in the region of one billion pounds, covering the police, the army and private security contractors. As well as the threat of a so-called spectacular attack linked to either Al Qaeda or dissident Irish groups, there are also concerns over public protest, serious organised crime and hoaxes.
There will be 10,000 police officers on duty at the Games, in addition to 10,000 on duty for the rest of London. A further 13,000 private security officers will also be deployed. Security checks are going to be as stringent as those at airports: every bag will be X-rayed and there will be a ban on umbrellas, horns, whistles, drums and any other device which might be considered disruptive.
The police, the army and the security services have been carrying out high-profile exercises over the months leading up to the games, acting out scenarios on the London Underground and preparing for operations over London's skies. The greatest fear is another event like Munich in 1972, when members of the Palestinian group Black September killed nine Israeli athletes. Recent events have also highlighted the threat of civil disobedience and lone protestors, determined to disrupt individual events.
The main Olympic site in Stratford is problematic in itself: intelligence sources say that if you were to ask MI5 to draw a heat map of terrorist suspects one of the hottest patches would be around the East London area - right by the Olympic site.
The BBC's Security Correspondent Gordon Corera draws on exclusive access and interviews with those charged with making sure the games run smoothly.
Producer: Mark Savage.