A worker cleans the Hyde Park memorial dedicated to the 52 people killed in the 7/7 terrorist attacks of 2005. (Niklas Halle'n/AFP/Getty Images)

When Gill Hicks unexpectedly ran into the police officer who helped save her life 10 years ago, the tears came quickly.

For many, memories of the 2005 London bombings remain fresh, etched into the collective psyche — and the reminders are stark. Hicks lost her legs in the coordinated terrorist attacks, the worst recorded on British soil.

Britain is marking the anniversary of the blasts, in which four suicide bombers targeted London’s public transportation system, killing 52 people and injuring more than 700.

Hicks was at the King’s Cross train station in central London on Monday, joining Jewish, Muslim and Christian leaders to commemorate the 10th anniversary with a short walk while carrying a white floral tribute arranged to read the word “Together.”

But just before the walk began, she was reunited with Andy Maxwell, the officer who a decade ago found Hicks fighting for her life in the smoke-filled subway train car where Germaine Lindsay, a 19-year-old sitting one person away from Hicks, had detonated a bomb, killing himself and 26 others.

Gill Hicks, a survivor of the 7/7 London terrorist attacks, embraces a police constable outside King’s Cross station in London. (Niklas Halle'n/AFP/Getty Images)

“It was very emotional seeing her again,” Maxwell said after hugging Hicks and kissing her forehead.

Several events this week mark the anniversary, including a Tuesday morning service at St. Paul’s Cathedral that was attended by Prime Minister David Cameron and London Mayor Boris Johnson. In Hyde Park, about 400 survivors and family members gathered Tuesday afternoon near a memorial of 52 steel poles, one for each victim of the attacks.

“The world can change in an instant. That’s what you learn,” said Richard Levy, 40, who was at the Hyde Park service. He suffered serious burns when one of the bomb blasts threw him against electric cables in a tunnel near the Russell Square station.

The commemorations have added poignancy because Britain is also mourning the loss of 30 of its citizens in a terrorist attack in Tunisia less than two weeks ago.

“Ten years on from the 7/7 London attacks, the threat continues to be as real as it is deadly — but we will never be cowed by terrorism,” Cameron wrote on Twitter.

On July 7, 2005, at 8:50 a.m., three bombers set off coordinated explosions that rocked the British capital: One bomb was detonated between the Liverpool Street and Aldgate subway stations, killing seven; another was set off at Edgware Road, killing six; and a third was detonated between King’s Cross and Russell Square, killing 26.

Almost an hour later, a fourth bomber climbed onto the top deck of a crowded double-decker bus in central London and blew himself up, killing 13 people.

The country was shocked to discover that the four bombers were British Muslims. The attacks became known as the 7/7 bombings — much like the 9/11 terrorist attacks in the United States. In the aftermath, multiethnic Britain rolled out a number of initiatives to fight radicalization, some of which remain deeply controversial.

In addition to the official events Tuesday, there was a campaign to encourage commuters to walk the last stage of their journey and to share their experiences on social media using the hashtag #walktogether.

Steve Ballinger, a spokesman for British Future, a think tank helping to promote the idea, noted that on the day of the bombings, many people “walked home calmly . . . and we wanted to take inspiration from that.”

Ann Cable, 62, said she was planning to mark the anniversary by getting off at the King’s Cross station, normally the penultimate stop in her commute, and walking the rest of the way to work. Cable, who was deputy commissioner for St. John Ambulance London at the time of the attacks, said her most vivid memory of that day was how her colleagues, after helping the wounded, simply sat in silence. “I remember the silence, and people just not wanting to talk,” she said.

Hicks, the survivor who lost her legs, flew to Britain from her native Australia to take part in memorial events. She has also set 10 challenges for herself this year, one of which is rappelling down a tall building alongside her best friend, Tracy Russell, a paramedic who was one of the first people to treat her.

The 47-year-old Hicks wears prosthetic legs and suffers from continual nerve pain. “It’s a shooting pain that comes off from the stumps,” she said in an interview. She said she has learned to think of the pain “as a reminder I’m alive and how wonderful I have a life and I can feel anything, so it’s part of the spectrum of being alive.”

After the bombings, she left her job as head curator at the Design Council and now runs an anti-extremism organization called M.A.D. (Making a Difference) for Peace.

Despite her optimistic demeanor, she said she is getting angrier with each passing year. “Absolutely, because it’s not okay, this horrific ideology that people would be willing to take their own lives . . . in a bid to kill and maim as many people as they can.”

But she said the difference between her anger and that of the bombers is that “my anger is positive.”

“My anger is a fuel that keeps me motivated, to ensure I keep getting up every day and saying my job is — I’m always an advocate for the benefits of peace and an advocate for terrorism not working,” she said. “It doesn’t work.”

Daniela Deane contributed to this report.