Britain fell silent for two minutes on Friday in memory of the victims of the London bombings, as its top policeman warned that the threat of more outrages has "palpably increased" in the year since then.
Fifty-two people died when four British Muslim suicide bombers, with explosives packed into rucksacks, blew themselves up inside three packed London underground trains and a double-decker bus on July 7, 2005.
It was the worst-ever terrorist attack on British soil, as well as Europe's first experience with a suicide bombing.
Midway through a day full of remembrance events, the nation observed two minutes' silence at noon (0430 IST), signalled by the tolling of the Lutine Bell at the Lloyd's of London insurance market.
Traffic came to a halt, and workers poured out of offices to line the sidewalks in a moving show of remembrance and solidarity.
Solemn commemorations began during the morning rush hour at King's Cross station, where a year earlier the four bombers -- Mohammad Sidique Khan, Shehzad Tanweer, Hasib Hussain and Jermaine Lindsay -- stepped off a commuter train and split up to carry out their deadly mission.
On the airwaves, meanwhile, Metropolitan Police commissioner Sir Ian Blair warned that London -- home to seven million people from countless nationalities, faiths and ethnic groups -- was not immune from another attack.
"Since July 7, the threat has palpably increased," Blair told BBC radio. "I fear we have to accept that we live in an age .
Extra police were seen deployed at underground stations, but Transport for London, which oversees the capital's mass transit system, said there was no sign of commuters and tourists shunning the Tube and buses.
"It's been very much business as usual," a spokesman said.
On the eve of the commemorations, Tanweer returned from the dead by way of a chilling videotape, aired on British television.
"What you have witnessed now is only the beginning of a string of attacks that will continue and become stronger," said Tanweer on the tape, which also featured Al-Qaeda's number-two Ayman al-Zawahiri and was apparently put together within the past five weeks.
The King's Cross commemoration was led by London Mayor Ken Livingstone and Culture Secretary Tessa Jowell, who laid wreaths at the moment of the first bombing -- 8:50 am -- then bowed their heads in tribute to the dead.
Many commuters paused to remember and to lay floral wreaths, not only at King's Cross but at the other bomb sites -- the Aldgate, Edgware Road and Russell Square underground stations and at Tavistock Square, where the packed red double-decker bus was struck.
Memorial plaques were unveiled at all the sites shortly before noon.
More than 1,000 people were expected to attend, and to hear a roll call of the victims.