The UK has been paying tribute to the victims of the 7 July London attacks, one year after suicide bombers killed 52 people and injured nearly 800.
Cathedral bells have tolled, flowers have been laid near the blast scenes and at noon the country fell silent for two minutes to remember the victims.
The day culminated in a service of remembrance at London's Regent's Park.
Prime Minister Tony Blair said the anniversary was an opportunity for "the whole nation to come together".
He said it was a chance "to offer comfort and support to those who lost loved ones or were injured on that terrible day".
The Regent's Park service included readings and songs dedicated to those who died in the attacks on three underground trains and a bus.
Poems were read by family members of those who died.
Attending the emotional event were Mr Blair, Conservative leader David Cameron and Culture Secretary Tessa Jowell.
Ms Jowell told the service London had suffered a "terrible atrocity".
"We all remember what happened that day and we will never forget," she said.
"So we have come together in an act of remembrance to pay our respects to those 52 people, each one loved, each one loving."
Members of the public laid flowers within a mosaic in Queen Mary's Gardens in the park.
After the Regent's Park service, survivors and the bereaved added their flowers to the mosaic, and the public can pay their respects over the weekend.
Earlier, Mr Blair joined emergency service workers in London for the silence, which was observed across the country.
Meanwhile, Metropolitan Police Commissioner Sir Ian Blair warned London must expect another attack.
"I know there will be further attacks, but as to whether we will stop those, well we've stopped three already," Sir Ian told BBC News.
Friday's commemorations began with London Mayor Ken Livingstone and Tessa Jowell laying flowers at King's Cross station at 0850 BST - the exact time of the three underground bombings.
The bells of London's St Paul's Cathedral tolled at the time of the Tube bombings, which happened near Aldgate and Edgware Road stations, and between King's Cross and Russell Square.
They also tolled an hour later to mark the fourth blast on the number 30 double-decker bus at Tavistock Square.
Memorial plaques were unveiled at King's Cross, Russell Square, Edgware Road, Aldgate and Tavistock Square.
Dr John Sentamu, the Archbishop of York, prayed for the victims of the attacks and their families as he opened a meeting of the Church of England's general synod.
The Queen attended St Giles Cathedral in Edinburgh, where bells rang out at noon to mark the anniversary.
Wales' First Minister Rhodri Morgan wrote a letter of condolence to Mr Livingstone on behalf of the Welsh population.
Other events have been held in private for victims' families and survivors.
7 JULY ASSISTANCE CENTRE
Confidential helpline to provide advice and support to anyone affected by events of 7 July or the anniversary
Phones manned 24 hours from 5-10 July
Centre and helpline open seven days a week at all other times - answerphone service at night
Also supports those affected by recent bombings in Doha, Sharm El Sheikh, Turkey, Bali and Dahab, and Bahrain boat disaster
Helpline - 0845 054 7444
Copies of a book of tributes, along with visitors' books for the public to sign, are going on permanent display at both St Ethelberga's Centre for Peace and Reconciliation and the Museum of London.
Three of the four bombers had links to the Beeston area of Leeds, where the city's first Asian lord mayor planted a "Tree of Hope" in the park where bomber Shehzad Tanweer played cricket just a few hours before setting off for London 12 months ago.
Meanwhile, the Muslim Council of Britain's secretary general, Muhammad Abdul Bari, joined calls for a government rethink over its decision not to hold an inquiry into the events of 7 July 2005.
"The narrative of events gives only a partial picture - we want to have a full picture," he said.
But Ms Jowell said the government would not hold a public inquiry because that would mean an "enormous diversion of security resources which need to be directed into preventing this happening again".
There has been a high-visibility police presence on the transport network during the day to reassure the public.
On Thursday, a video of Shehzad Tanweer was aired on al-Jazeera television. It showed the 22-year-old warning of further attacks.
The 7 July Assistance Centre can be contacted on 0845 054 7444.