LONDON -- Police thwarted a major terrorist plot yesterday, discovering two Mercedes cars loaded with nails and canisters of propane and gasoline set to detonate and kill possibly hundreds in London's crowded theater and nightclub district.
The plot was discovered two days after Gordon Brown took over as prime minister, and just before the anniversary of the attacks on July 7, 2005, when the London Underground and a double-decker bus were targeted by a group of homegrown terrorists who killed 52 people.
Nobody claimed responsibility for the latest plot, and government security officials said late yesterday that no suspects have been identified.
As police searched for car bombs and terrorists in the city of 7.5 million, roads were closed and police sirens echoed. Authorities stepped up security across Britain, from central London streets to the Wimbledon tennis tournament.
But Londoners -- who have experience in dealing with bombs and terrorism -- were not in hiding and the West End was bustling again by nightfall yesterday.
"I know you can't live your life being scared," Natalie Huntley, 28, a tourist from Adelaide, Australia, said outside St. Paul's Cathedral even as police investigated another suspicious vehicle parked on nearby Fleet Street. "You've just got to keep going, don't you?"
Authorities said the bombs in both cars were similar and that each had been abandoned in the same area near Piccadilly Circus. Had they exploded, hundreds of people might have been killed.
The discovery of the car bombs before they exploded allowed police to check for fingerprints and DNA clues, as well as other trace evidence. They also had footage from closed-circuit TV cameras, hoping the surveillance network that covers much of central London will help them track down the drivers.
The CCTV footage would be compared with license plate recognition software, Peter Clarke, British antiterror police chief, said. There are 160 security cameras in the Westminster Council, the district encompassing Piccadilly Circus and the Haymarket area, alone.
The discovery of the second bomb, about 20 hours after the first, suggested a coordinated and more sophisticated plot than was initially thought -- similar to the 2005 suicide bombings in which four bombs exploded within an hour of one another on London's transit system.
Some analysts said the bombers could be trying to send a message to Britain's new leader.
"It's a way of testing Gordon Brown," said Bob Ayers, a security specialist at the Chatham House think tank. "It's not too far-fetched to assume it was designed to expedite the decision on withdrawal [from Iraq]."
After the first bomb was announced, Brown said "we face a serious and continuous security threat in our country."
Professor Paul Wilkinson, chairman of the Center for the Study of Terrorism and political violence at St. Andrews University, said a number of factors could have come together to prompt the thwarted attacks.
"With the change in prime minister this could be the work of Al Qaeda," he said. "They have a track record of trying to influence political change through violent means such as in the Madrid train attacks.
British officials said they had not established a connection to any terrorist organization, and there had been no prior intelligence of a planned attack by Al Qaeda.
US authorities said there was no specific terror threat to the United States, and the national alert level, currently at yellow (elevated), was not raised.
The busy Haymarket thoroughfare linking Piccadilly Circus in the heart of London's theater district and near Trafalgar Square has many restaurants, bars, a cinema complex, and West End theaters. It was packed with people at the time.
It was ladies' night Thursday at the massive Tiger Tiger nightclub, a three-story venue that can pack in 1,770 people and stays open until 3 a.m. It was here that the explosives-laded car was parked closest.
The events unfolded when police were called to Haymarket at 1:30 a.m. yesterday. A man fell at Tiger Tiger, injuring his head, and an ambulance crew noticed smoke coming from a car parked in front of a club.
The announcement of the second bomb came after police had closed off Park Lane along Hyde Park for several hours to investigate a suspicious Mercedes. That car had been towed across town to an impound lot; the attendants there, on the alert after news of the first foiled car bombing, smelled gasoline and alerted authorities.
The car had been parked on Cockspur Street, which runs between Haymarket and Trafalgar Square. About 2:30 a.m., it was ticketed and then towed an hour later to the impound lot on Park Lane on Hyde Park's eastern edge, Clarke said.
The car was removed from the scene after a bomb squad manually disabled the explosives.
The bomb was powerful enough to have caused "significant injury or loss of life" at a time when hundreds were in the area, Clarke said.