British police stepped up their patrols in London this morning after the discovery of two car bombs packed with petrol, gas and nails in the capital's teeming theatre district.
Authorities launched a counter-terrorism investigation after yesterday's discovery of explosives in two parked Mercedes cars in London's West End that had echoes of an earlier al Qaeda plot.
With high profile events scheduled in London at the weekend including a Gay Pride march, the Wimbledon tennis championships and a concert in honour of Princess Diana, police maintained a high alert.
"There will be more police patrols. The investigation is moving ahead," anti-terrorism police chief Peter Clarke said.
Tens of thousands of people were expected to attend the Gay Pride march which will follow a route from Baker Street to Trafalgar Square today.
Wimbledon tennis would also continue following a review of security arrangements, police superintendent Peter Dobson said.
Detectives were checking CCTV footage from the area around Haymarket and Cockspur Street where the two cars were discovered and carrying out forensic tests.
A combination of luck and quick thinking helped security services avert attacks that could have killed or maimed scores.
Officers defused the first in a green Mercedes parked outside one of London's biggest nightclubs, the cavernous Tiger Tiger, at around 1am. The club was packed with hundreds of people 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. It contained gas tanks, fuel cannisters and nails.
Similar material was later found in a blue Mercedes that had been parked illegally nearby and
towed to a garage in Park Lane. The two cars were "clearly linked", Mr Clarke said.
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," Mr Clarke said.
He added 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 in 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.
"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.
Sky News said the first device was rigged to detonate with a mobile-phone trigger. Police would not confirm that report.
Intelligence sources said they could not rule out an al Qaeda link. A security source said: "The balance of probability does lie pretty strongly with international terrorism."