Keeping the Olympic Games safe is the biggest security operation since World War II. It has been planned for years, involves 40,000 people and will cost more than £1bn. After the failure of G4S, correspondent Gorden Corera investigates where or not London is on track. For a Radio 4 documentary, Securing the Games, he has been granted exclusive access to the preparations taking place.

Chris Scott from Home Office security said that it is important to "stress the system to prove that it works against any scenario". He added that they are "trying to recreate the context of panic to test how they would respond".

The department's head of counter-terrorism and terrorism, Charles Farr, said that the "first priority is the safety of the public, and beyond that games continuity is a key factor. I don't envisage a crisis but we have all the arrangements in place."

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