Scotland Yard's anti-terrorist branch is appealing for information on the whereabouts of a taxi in the hours before a bomb it was carrying exploded outside the BBC Television Centre in west London at 12.30am on Sunday.

Head of the anti-terrorist branch Deputy Assistant Commissioner Alan Fry believes the red vehicle, which was bought from Edmonton at 9.30am on Saturday, may then have been driven through the borough by the Real IRA on the North Circular or M25 and hidden in a rented or borrowed lock-up garage.

The taxi had a registration number D902 GYH, a distinctive silver-coloured steering wheel and advertisement for the Benihana restaurants on its side.

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Mr Fry said: "Somewhere the cab was packed with explosives between about 9.30am on Saturday morning and 10.40pm that evening. Did you see a red cab parked in any unusual circumstances? Did you allow someone to use accommodation or a lock-up? Did you follow a red cab which had no licence plate?"

Operations Chief Inspector Bob Parkinson at Barnet Borough Police added: "This taxi may have been driven through the borough, which has been targeted by the IRA before, and someone somewhere must have seen this car being driven by the bomber."

Chf Insp Parkinson reassured residents that police are on a high state of alert and added: "I'm urging residents to be vigilant against the threat of further terrorist attacks and it's essential people are alert and report anything suspicious to the police. But don't let these terrorists stop you from doing your normal daily activities."

If you have any information call the 24-hour confidential hotline on 0800 789 321