Counter-terrorism police immediately launched an investigation into the hoax security incident to face Gordon Brown since he became prime minister.

Sky News quoted unidentified sources as saying cctv had captured an image of the hoaxer as he got out of the car.

Defence Secretary Des Browne told BBC Radio Scotland: "It does appear to be a very serious incident involving our friends beside the river. My first reaction to this is, thank God they cannot make a real bomb and that nobody has been injured while they were running back to MI6 buildings."

The Government's Cobra emergency response committee - bringing together ministers, officials and experts but excluding Scarlett- was to convene in response to the threat.

The committee will then brief Mr Brown's new Cabinet, which was due to meet later.

One witness said door staff at the Tiger Tiger nightclub alerted police after the car was driven into bins last night and a bald driver fled.

The witness said the large silver saloon car was being driven erratically before the minor crash and Scarlett was drunk and shouting "Evelyn made me do this."