Makeshift shrines and piles of roses and daisies adorned the front of the Kings Cross rail station, one of the sites of the July 7, 2005, coordinated attacks on three subway trains and a bus. Mourners started laying the first flowers at 8:50 a.m., the exact time of the first attack.
Tim O'Toole, the London Underground managing director, laid a wreath with a note reading, "We will never forget. We shall continue to serve."
A second ceremony began nearly an hour later at Tavistock Square, where the fourth bomb exploded at 9:47 a.m. aboard the No. 30 bus.
"It's so strange, because I can remember exactly what I was doing this time last year. Everything was all normal and then suddenly, it was not. People were going about their normal daily business and then bombs were going off," said Angelina Alcorn, 26, a nurse at nearby University College Hospital who helped many of the injured. "I will never forget the image of that bus. It is stuck in my mind."
Blair, who attended a private memorial at London's Fire Brigade headquarters during the nationwide silence at noon, said he hoped the public would also pay tribute to the efforts of emergency service workers during the bloodshed.
"This is a time when our country unites across all races, religions and divides and stands in solidarity with all those who have suffered so much, in sympathy with them and in defense of the values which we share," Blair said.
"It is also an opportunity to reflect on the extraordinary efforts of our emergency services, transport staff, health workers and members of the public, whose courage, professionalism and humanity won the admiration of the world."
"London's still the vibrant city I know. I love it to bits. And I love the people. And the defiance, the sort of attacks won't change our way of life," Michael Henning, who survived the attacks, told CBS News correspondent Sheila MacVicar.
Play at the Wimbledon tennis tournament halted for the two-minute commemoration. Memorial plaques were unveiled at each of the four Underground stations affected by the attacks. Later Friday, the names of the 52 dead were read aloud during an evening service in flower-filled Regent's Park.
Also on Friday, Al Qaeda No. 2 Ayman al-Zawahiri said that London bombers Shehzad Tanweer and Mohammad Sidique Khan hadand spent time at a camp to prepare themselves for a suicide attack, new video excerpts released Friday claim.
On the eve of the anniversary, aof one of the suicide bombers threatening more terror was broadcast by the TV network Al-Jazeera. It was unclear how the video was obtained or how soon before the attacks it was made.
"What you have witnessed now is only the beginning of a series of attacks that will continue and increase in strength," said Tanweer, 22, whose backpack bomb killed six people and himself aboard a Circle Line subway in east London.
"The release of this videotape is a timely reminder that two of the four 7/7 suicide bombers — ringleader Khan and Tanweer — are the strongest candidates for real al Qaeda connections to the attacks that killed 52 civilians in London," adds CBS Evening News investigative producer Phil Hirschkorn. "Yet one year on, according to the U.K. government, 'The extent of al Qaeda involvement is unclear.'"
Terence Clark was at King's Cross to remember his 27- and 31-year-old cousins, who died on the Picadilly line train. "Why did they have to show the video last night?" he said. "Why can't they leave us in peace? We lost our loved ones and we are serving a lifetime sentence."
The huge police presence in London that immediately followed the attacks has abated, but security remains tight.
The coordinated assault was the first suicide attack in Western Europe as well as the deadliest attack in London since World War II. 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.
Many British Muslims feel they're targets for suspicion; rights activists fear new anti-terror powers threaten civil liberties; and two mistaken shootings by officers have undermined public trust in the police.
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.
Tanweer's video arrived at an Al-Jazeera office with clips showing Osama bin Laden and al Qaeda's No. 2 leader, Ayman al-Zawahri. The terror network has claimed responsibility for the London attacks, but authorities say it's unclear what its role was.