Former British prime minister Tony Blair voiced "sorrow, regret and apology" after a damning report on the Iraq war Wednesday, but said he did not mislead parliament and did not regret toppling Saddam Hussein.

"I express more sorrow, regret and apology than you may ever know or can believe," said Blair, his voice breaking with emotion in a speech in central London.

However, he added: "As the report makes clear there were no lies, parliament and cabinet were not misled, there was no secret commitment to war.

"The intelligence was not falsified and the decision was made in good faith."

Blair made his comments at a press conference in London after publication of the long-awaited Chilcot report into Britain's role in the 2003 US-led invasion of Iraq sharply criticised him.

The former premier said the decision to take Britain to war was the "most agonising" he had ever taken, adding: "I will never agree that those who died or were injured... made their sacrifice in vain".

"I knew it was not a popular decision... I did it because I thought it was right and because I thought the human cost of inaction... would be greater for us and for the world in the longer term," he said.

If Iraqi dictator Saddam had been allowed to remain in power in 2003 "he'd have once again threatened world peace," Blair said, rejecting claims that the war itself increased the terror threat.

"Saddam was himself a wellspring of terror," he said.

"At least in Iraq, for all its challenges, we have today a government that is elected, is recognised as internationally legitimate," he added.