It is the second meeting of the committee bringing together ministers - including Home Secretary Jacqui Smith - with senior police, security service agents and Whitehall officials to co-ordinate operations to catch the bombers and maintain security.

The meeting came as London Mayor Ken Livingstone warned that the capital faced "a very real threat" of further terrorist attack, and called on Londoners to be "vigilant".

Unconfirmed reports from the USA suggest that police have obtained a "crystal clear" CCTV image of a suspect staggering away from a car after parking it outside a nightclub in the West End of London.

Scotland Yard declined to comment on the reports, which relate to a Mercedes packed with petrol, nails and gas canisters. It was left outside the Tiger Tiger club in Haymarket in the early hours.

Police said the car was "clearly linked" to a second Mercedes which was discovered nearby in Cockspur Street before being unwittingly towed away by parking wardens to an underground car park off Park Lane.

Detectives are searching the two vehicles for forensic evidence and examining hundreds of hours of CCTV footage for hints about the identities of the bombers.

The two fully intact car bombs hold vast numbers of clues about the people behind a suspected terrorist plot that could have killed hundreds.

Earlier, Mr Brown went to New Scotland Yard for a briefing from senior officers on the progress of their inquiries.

A Downing Street spokesman said: "It was a private meeting. Mr Brown was briefed on the current security situation and thanked frontline staff."