LONDON (Reuters) - Police found two car bombs packed with petrol, gas and nails in London's teeming theatre district on Friday, averting attacks that echoed an earlier al Qaeda plot and could have killed or maimed scores of people.
Officers defused the first bomb, found in a green Mercedes parked outside one of London's biggest nightclubs, the cavernous Tiger Tiger, at around 1 a.m., when hundreds were packed inside for "Sugar 'n Spice Ladies Night".
The police, alerted by ambulance workers who thought they saw smoke inside the car, defused the first bomb at the scene, saying it contained gas tanks, fuel canisters and nails.
Similar materials were later found in a blue Mercedes that had been parked illegally nearby and towed away. The two cars were "clearly linked" said Peter Clarke, London's anti-terrorism police chief.
"The discovery of what appears to be a second bomb is obviously troubling and reinforces the need for the public to be alert," he said.
Authorities said they did not know who left the bombs but they had begun a counter-terrorism investigation. The alerts came less than two years after Islamist suicide bombers killed 52 commuters on London transport.
"It is obvious that if the device had detonated there could have been significant injury or loss of life," Clarke said.
He said there were similarities between Friday's incident and an earlier plot, uncovered in 2004, in which an al Qaeda militant planned to detonate gas-fuelled bombs in limousines.
The ringleader of that plot, Dhiren Barot, was convicted last year. Another group of Islamic radicals were convicted this year for a plot in which a big nightclub was among the targets.
Prime Minister Gordon Brown, facing a major challenge two days after succeeding Tony Blair, convened Britain's top security committee, Cobra.
"SERIOUS AND SUSTAINED THREAT"
"We are currently facing the most serious and sustained threat to our security from international terrorism," Jacqui Smith, Brown's new home secretary, said after the meeting, which she chaired in her first day on the job.
A large area around the scene on central London's Haymarket street, near Piccadilly Circus, was sealed off during the day.
The area near the garage where the second car had been taken was also closed for much of the day but was later reopened.
Television pictures showed a gas canister after it had been removed from the first car. It was green and labelled "PATIO GAS", which is readily available at hardware stores.
Sky News said the first device was rigged to detonate with a mobile-phone trigger, but police would not confirm that report.
Britain has experienced an increase in terrorism-related threats since the September 11 attacks on the United States and since it joined forces with U.S. troops to invade Iraq in 2003, an event that provoked widespread domestic criticism.
Brown has pledged to respect Britain's commitments in Iraq, although there has been speculation he may accelerate the British troop withdrawal.
Intelligence sources said they could not rule out an al Qaeda link to the car bomb, and said the danger of international Islamist terrorism was the main reason Britain's threat level is placed at "severe", the second highest rating.
Brown said the incident showed the need for vigilance.
"The first duty of a government is the security of the people and as the police and security services have said on so many occasions, we face a serious and continued security threat to our country," he told reporters.
Security around parliament was stepped up, with police body-searching the drivers of cars entering the compound. Across town security was tightened at the Wimbledon tennis championship.