British investigators are examining images from security cameras in central London where two unexploded car bombs were found Friday.
The detectives are trying to identify the people who drove the cars full of gasoline cans, propane canisters and nails into London and left them in the busy entertainment district near Piccadilly Circus.
British intelligence sources say the police did not have any advanced warnings about the threat of car bombs.
The head of London's anti-terrorism police, Peter Clarke, said the first car bomb was found outside a crowded night club, where a blast could have resulted in many fatalities and injuries.
A second vehicle parked illegally in the area was towed to an impound lot near Hyde Park, where police discovered it also contained fuel canisters and nails. Clarke said the two incidents are clearly linked.
Britain's new Prime Minister Gordon Brown convened an emergency security meeting.
Mr. Brown said Britain faces a serious and continued security threat, while Home Secretary Jacqui Smith urged citizens to be alert and vigilant.
Next week, Britain marks the second anniversary of the July seventh London transit bombings, in which four Muslim suicide bombers set off explosions that killed 52 bus and subway passengers.
Some information for this report was provided by Reuters and AFP