London's sweaty subway cars are as jam-packed as ever this summer and red double-decker buses still roll through the capital crowded with commuters and photo-snapping tourists.

A year after homicide bombers brought carnage and chaos to three Underground trains and one of the city's iconic buses, life in the capital has returned to normal — almost.

The fear isn't entirely gone. It's just covered over by a veneer of calm, an uneasy sense of normality that could be shattered by another attack.

Britons got an unnerving reminder of their vulnerability Thursday, a day before the anniversary of the attacks, when al-Jazeera television broadcast a video made by one of last year's bombers promising more terror.

"What you have witnessed now is only the beginning of a series of attacks that will continue and increase in strength," said Shehzad Tanweer, 22, whose backpack bomb killed seven people and himself aboard a Circle Line subway in east London.

Memories of July 7, 2005, when an ordinary Thursday morning commute turned horrific, are never far from the surface. The bombs, which killed 52 commuters and injured 700, have changed Britain in ways large and small.

News that the four young attackers were all born or raised in Britain stunned many and strained ties between the country's large Muslim community and the wider population.

Rights activists, meanwhile, worry new anti-terror powers threaten civil liberties, and two mistaken shootings by officers have undermined public trust in the police.

Londoners were hardened by years of Irish Republican Army bombings in the 1980s and early '90s. And fearful or not, many must rely on public transportation in a city where taxi fares and parking costs are high.

"Terrorism has always been a factor and will always be a threat in this country, but I can't be scared," said Jason Dolby, 18, on his way into Oxford Circus station. "I've got to ride the Tube everyday to work, so there's no avoiding terrorism if it's going to happen."

Some people have been deeply shaken.

David Warman, 35, helped emergency workers after a No. 30 bus blew up in north London's Tavistock Square and still suffers nightmares. "I've never sat on a bus since. I won't even stand near one," he said.

Underlining the continuing danger, police said this week that they are investigating 70 suspected terrorist plots across Britain and the world.

"The threat is very real indeed," said Sandra Bell, an anti-terror expert at Britain's Royal United Services Institute, a security think tank.

Within days of the bombings, detectives identified those they believed responsible — four young men dead in the wreckage with their victims. Three were of Pakistani descent and lived in and around the northern English city of Leeds. The fourth was a Jamaican immigrant who settled northwest of London.

But a year later, police don't know to what extent others may have aided them and the search for a wider network appears stalled. No co-conspirators have been arrested.

Tanweer's video arrived at al-Jazeera's office with clips showing Usama bin Laden and Al Qaeda's No. 2 leader, Ayman al-Zawahiri. The terror network has claimed responsibility for the London attacks, but authorities say it's unclear what its role was.

A recent government report said investigators had uncovered no links between the attacks and a set of failed bombing attempts two weeks later, for which five men are awaiting trial.

The huge police presence in London that immediately followed the attacks has largely vanished, but security remains tight. Terror fears have even touched the Wimbledon tennis tournament, where police this week are using mirrors to check cars' undersides for bombs.

The government has enlisted moderate British Muslim leaders to help combat militant views, but police missteps appear to have antagonized many.

Two weeks after the bombings, officers fatally shot an innocent Brazilian man they mistook for a terrorist.

On June 2, about 300 police raided an east London home where they suspected a chemical bomb was being built, shooting one man in the shoulder before arresting him and his brother. Both were later released without charge.

Asaf Hussain, a lecturer on Islam at Leicester University, said the raid fed the fears of British Muslims that they are all suspects.

"For those people who are potential terrorists, they will say: 'Look, we'd better do our action, look how much they hate us,"' Hussain said.

The law too has changed.

Prime Minister Tony Blair pushed several contentious new measures through Parliament. Lawmakers resisted his demand to let police hold terror suspects without charge for up to 90 days, but did extend the permitted detention period from 14 days to 28.

The government won a provision barring the glorification of terrorism, which Blair says is crucial to fighting militant ideologies.

Shami Chakrabarti, director of the advocacy group Liberty, called both measures counterproductive. But she said they were less damaging than those in an even more sweeping anti-terror bill passed after the Sept. 11 attacks on America.

"Britain had a shock on 9/11," she said. "The 7th of July was an aftershock."