Ken Livingstone and Tessa Jowell laid flowers at King's Cross station

The prime minister joined firefighters in London for the two-minute silence.

Mr Blair said it was a time when the whole country united across races and religions to offer comfort to those who had lost loved ones.

Liberal Democrat leader Sir Menzies Campbell said it was a "day of sadness and reflection" for the UK.

Saluting bravery

As the nation fell silent at 1200 BST, Mr Blair joined the commemoration at the London Fire Brigade headquarters while Home Secretary John Reid was with police outside New Scotland Yard.

Earlier, Culture Secretary Tessa Jowell and London Mayor Ken Livingstone had been among those laying wreathes at King's Cross station, from where the four bombers set off on the underground last year.

It is a chance 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 Tony Blair

Mr Livingstone told the BBC News website people should pledge never to forget those whose lives were ruined by 7 July.

"But we should also take the greatest pride in the character of our capital city," he said.

In a statement issued by Downing Street, Mr Blair said: "Today is a day of remembrance across London and the United Kingdom.

"It is a chance 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 defence of the values we share."

'Calm determination'

In his statement, Sir Menzies said: "Our thoughts are with all the families and loved ones of those people who died and were injured in the bombings.

"We also remember the bravery of many members of the emergency services, train and utility workers and ordinary citizens on that terrifying morning one year ago today.

"It is part of the British character to meet tragedy with calmness and resolution.

"I have no doubt that we shall see these qualities on display in abundance, today and in the future."

Some of the survivors and families of the victims have renewed their calls for a public inquiry into the bombings.

Ms Jowell ruled out an inquiry, saying she did not think it would answer all the unanswered questions and would be an "enormous diversion" for the security services.

She promised she and the home secretary would continue to meet victims' families to answer their questions as fully as possible.