Police have a 'crystal clear' video image of a man who tried to kill hundreds of people by blowing up two cars in central London, according to reports.

After a second bomb was found yesterday, there are now fears that other bombs could be primed and parked around the capital.

An American television report said investigators already know the face of one of the men responsible, but police - who are still studing footage from hundreds of CCTV and congestion charge cameras - are refusing to confirm this.

It's thought the image shows the man "staggering" from the first car after parking it outside a West End nightclub.

Prime Minister Gordon Brown today chaired a meeting of the Government's emergency Cobra committee to consider the official response to yesterday's failed car bombs.

It was 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".

Mr Brown this morning 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."

Mr Livingstone urged Londoners to keep their eyes peeled for anything out of the ordinary which might indicate a follow-up attack.

"The discovery of two potential car bombs in central London, with those responsible still at large, means we face a very real threat of terrorist attack at this moment in time," he said.

"It is imperative that all Londoners are vigilant and provide any information at all which may have any possible relevance to the Metropolitan Police immediately."

Speaking after the Cobra meeting, Ms Smith said: "We were updated on the police operation and the Prime Minister took the opportunity to thank the police and the security services for all their hard work over the last 48 hours.

"The Prime Minister stressed that all parts of Government have got to work together to combat the terror threat. I am satisfied that across Government and with the police and agencies, we are doing all we can to protect the public.

"The police are clear that the most important contribution that the public can make is to carry on reporting anything suspicious and to be vigilant, and I would ask them to do that.

"But I must stress that we mustn't let the threat of terror stop us from getting on with our lives." Communities Secretary Hazel Blears, who attended the meeting, said: "It's essential we all stand together against those who threaten our way of life.

"I'm most encouraged by the support shown by leaders of our Muslim communities across the country."

The second petrol, gas and nail bomb was discovered in a Mercedes towed to a car pound after being found illegally parked in the West End.

The vehicle had been left just yards from the spot outside a nightclub where two bomb-disposal officers risked their lives to make the first rigged car safe.