Much of Britain fell silent for two minutes at midday (1100 GMT) Friday as the country marked the painful memory of the worst bombings in London since World War II.
Prime Minister Tony Blair observed the silence with members of the emergency services who led the response to the attacks of July 7, 2005.
Queen Elizabeth II, Prince Philip and Prince Charles stood in silence at a service in St Giles' Cathedral in Edinburgh.
Earlier wreaths were laid and commemorative plaques unveiled close to where the bombs went off on London's Tube and at the site of the bus bombing, Tavistock Square.
"The memories are still very profound and vivid in my mind," Tube passenger Neesha Kamboj told CNN.
"It was at 8:50 this time last year that our carriage was plunged into darkness, dense billowing smoke came into the carriage... we couldn't hardly see, we couldn't hardly breathe, we were choking, people were panicking -- it was carnage really."
Nonetheless, CNN's Christiane Amanpour reported, Londoners continued to show their defiance of the terrorists by using the Tube system as normal on the anniversary of the attacks. There was no marked shortfall in the one million passengers using the system by the middle of the capital's rush hour.
Under the great dome of St. Paul's Cathedral, as its bells tolled, candles were lit at the exact time the four bombs went off -- the first at 8:50 a.m. (0750 GMT).
At King's Cross station floral tributes were laid by Cabinet minister Tessa Jowell, London mayor Ken Livingstone and London Underground managing director Tim O'Toole.
After laying their wreaths, they stood solemnly in silence, heads bowed, to honor the 52 innocent people who lost their lives in the attacks.
The commemorative events moved on to Tavistock Square, where 13 died in the explosion on the No. 30 bus.
Livingstone was joined by George Psaradakis, 50, the Greek-born driver of the number 30 bus that was ripped apart by one of the bombs. The wreckage became one of the defining images of the carnage.
At exactly 9.47 a.m (0847 GMT), the time of the final blast, Psaradakis laid a memorial wreath in tribute to the victims, reading: "You will never be forgotten. May you rest in peace."
At Russell Square Underground station near the Kings's Cross blast, Tube staff stood silent. Among the people who laid flowers at the scene was 30-year-old Susan Harrison, who lost a leg when the bomb exploded close to the carriage she was travelling in.
At Aldgate station, where a year ago a steady stream of casualties was dragged from the smoke, travelers slowed or stopped momentarily to pay their respects. Some added to the burgeoning collection of flowers that were being laid outside neighboring St. Botolph Church.
At Edgware Road the station manager organized a floral tribute for the families comprised of irises and carnations.
Mass of flowers
A memorial service was taking place at London's Regent's Park beginning at 6 p.m. (1700 GMT).
In the park there was a huge floral tribute. A seven-petal flower template, 40 feet across, was set up in Queen Mary's Garden near the site of the memorial service.
The template quickly filled as people stopped off on their way to work or passed through the park to take part in the flower laying.
One woman who lives in apartments near the park said the scene brought back many memories of the "silence, stillness and quietness" following the explosions as traffic and other activity in the capital came to a standstill.
She told the UK's Press Association: "This shows people how strong we are in this country. It just shows how many people still remember but it lets them remember and then get on with things, that's what we do."
Prime Minister Blair said in a statement that the anniversary of the 7/7 attacks was an opportunity for "the whole nation to come together to offer comfort and support to those who lost loved ones or were injured on that terrible day."
"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 we share."
The memorial day came one day after a videotape was aired on Al-Jazeera television in which one of the suicide bombers said there would be more violence.
"What you have witnessed now is only the beginning of a series of attacks that will continue and pick up strengths till you pull your soldiers from Afghanistan and Iraq and stop your financial and military aid to America and Israel," said suicide bomber Shehzad Tanweer, 22, who delivered what was called his last will and testament in English.
He was killed in the July 7, 2005 attack.
CNN terrorism analyst Peter Bergen said the latest video is more evidence that "the London attacks were a classic al Qaeda operation and not the work of self-starting terrorists as has been repeatedly suggested in the media."
British newspapers expressed outrage at the timing of the video's release.
"Damn You To Hell," the Daily Mirror said in its banner headline on Friday beside a picture of Tanweer.
The Daily Mail called it "a cynical ploy to hijack the news agenda on the anniversary of the massacre."
On its front page it carried pictures of every one of the 52 victims of the bombers and said: "Yesterday, those behind the 7/7 atrocity released a video of one of the bombers. Their aim, on this poignant anniversary, was to keep the victims of their evil act off the front page. They failed."
The Sun newspaper paid tribute to Britain's defiance against the bombers with a photo of a number 30 London bus with the destination board: "30. Aldgate- Edgware Rd-King's Cross-Tavistock Sq. UNBEATEN."
London Transport say there was no discernible drop-off in passengers on the Tube Friday morning. They say they carried over one million passengers on 500 trains by 9.00 a.m., the normal figure.
Survivors of the bombings say the official report into the attacks, published in May, did not answer all their questions. Many want a full public inquiry into the day which, like the September 11 attacks in the United States, has become etched into the British psyche as a simple but potent date -- 7/7.
Four men were arrested after police said they thwarted a similar attack on July 21 last year when bombs failed to explode.
Metropolitan Police Commissioner Ian Blair said that the threat of further terrorist attacks in the UK had "palpably increased" and the possibility of another attack was "very real".