A mocked-up terror attack on the London Underground is being staged today as part of a massive exercise to test security for the 2012 Games.
The exercise is to test the response to a terrorist incident on the London Underground network during the Olympics.
Some 2,500 people - spanning everyone from constable to Cobra, the top level government committee which sits during national emergencies and crisis, are being put through their paces by the two-day test.
The disused Aldwych station, a stone's throw from central London's Royal Courts of Justice, will be the scene of the live test.
Much of the action is taking place behind closed doors.
The test is being staged as if it is August 8 and 9 - two busy days during the Olympics.
National Olympic Security Coordinator, Assistant Commissioner Chris Allison said: "Testing and exercising is vital to getting our safety and security operations for the Games right.
"We need to be confident that we have the right people in the right places, that we understand how others operate and that we are talking to each other at the right levels and in the right way.
"This is part of series of exercises which we have run in the lead up to the Games, but this is the first with such a significant response from the emergency services on the ground.
"The initial incident will test the tactical response including evacuation the station, rescuing injured people and managing the crime scene.
"The exercise will go on to test how senior decision makers manage the impact of the incident, the investigation to catch those responsible and a range of issues such as travel disruption, protest and organised crime which may impact on the smooth running of the Olympic Games."
Crime and Security minister James Brokenshire said: "We want to deliver a Games where the sporting achievement and the Olympic spirit is what people will remember - not the security.
"To ensure that happens we need to test our plans and this exercise gives us the opportunity to inform, reassure and build confidence in the UK's safety and security operation.
"We are determined to leave nothing to chance to deliver a safe and secure Games that London, the UK and the World can enjoy."