Sir John appealed for calm as a heckler shouted: "What, no regrets? Come on!" His voice fading, Mr Blair insisted that Britain - especially its armed forces - should feel an "immense sense of pride" over the Iraq war. He added: "I had to take this decision as Prime Minister. It was a huge responsibility and there is not a single day that passes by that I don't reflect and think about that responsibility." He insisted that the war, which cost the lives of 179 British soldiers, was justified despite the failure to uncover any weapons of mass destruction.

Mr Blair even predicted that Western leaders might be forced to invade Iran, as it presents as serious a threat today as Iraq did under the rule of the "profoundly wicked, almost psychopathic" Saddam seven years ago.

The former prime minister closed his long-awaited appearance before the Chilcot inquiry by arguing that the world was a safer place following the war. Members of the audience, who included the families of dead servicemen and women, yelled "murderer" and "liar" at him, while several were led out of the hearing in tears.

Mr Blair admitted making mistakes in preparing for the aftermath of the invasion and in presenting the case for war. But he was otherwise unrepentant about joining the US-led military action in March 2003, making plain he was preparing to send British troops into Iraq long before the invasion began. Although weapons of mass destruction were never uncovered in Iraq, Mr Blair argued that Saddam "retained absolutely the intent and the intellectual know-how to restart a nuclear and a chemical weapons programme". He repeatedly singled out Iran as he warned the current generation of world leaders that they face a similar dilemma today, adding that his fears at the time - that failed or highly repressive states with WMD "become porous, they construct all sorts of different alliances with people" - were even stronger now "as a result of what Iran particularly is doing".

Police mounted a massive security operaton outside the QEII Conference Centre in Westminster as Mr Blair was smuggled in through a rear entrance to give evidence. Before the cross-examination began, Sir John Chilcot, appealed to members of the audience not to heckle Mr Blair - and warned his witness to be truthful.

Once the questioning began, the former prime minister fiercely denied misleading the country in the count-down to war. He said: "This isn't about a lie or a conspiracy or a deceit or a deception. It's [about] a decision."

Mr Blair dismissed claims by Sir Christopher Meyer, the former British ambassador to Washington, that he had secretly committed to join an invasion when he met George Bush at the President's ranch in Crawford, Texas, in April 2002 - almost 11 months before the war began. He insisted that he had said nothing in private that he was not saying in public - adding that Sir Christopher was not at the meeting.

Mr Blair said that during the meeting he was still pressing - despite US scepticism - for a fresh attempt to bring Saddam to heel though the United Nations. But when asked what message he believed Mr Bush took from the talks, he said: "Exactly what he should have taken - if it came to military action because there was no way of dealing with this diplomatically, we would be with him."

Mr Blair told the inquiry he believed the "calculus of risk" posed by rogue states changed completely following the attacks of 11 September 2001. Before then the international community had relied on a "hoping for the best" strategy of containing Saddam Hussein through targeted sanctions and enforcing a no-fly zone over Iraq. But he admitted that it was the "risk calculation" that had altered since 9/11, rather than the intelligence about WMDs.

Apparently contradicting assertions at the time about the "growing" threat from Saddam, Mr Blair said: "It wasn't that objectively [Saddam] had done more ... It was that our perception of the risk had shifted."

Later Mr Blair said he stood by his use of the word "growing" in the September 2002 dossier making the case for war, pointing to claims (that were subsequently disproved) that Saddam had mobile units for unleashing biological weapons. Mr Blair, who said the dossier was regarded as "somewhat dull and cautious at the time", also maintained he was right to assert in the document that it was "beyond doubt" that Saddam had developed WMDs. Mr Blair told the inquiry: "I did believe it. I did believe, frankly, beyond doubt."

Mr Blair did acknowledge that the Government should have made clear that the notorious claim Saddam could launch weapons within 45 minutes referred to battlefield munitions rather than long-range missiles.

He said newspaper reports focusing on the 45-minute claim should have been corrected. But in a reference to the battle between the Government and the BBC over the claim, and the death of weapons scientist David Kelly, he said the issue took on a "far greater significance" in the light of later events.

He admitted that the coalition made two crucial mistakes in planning for the aftermath of the invasion - not catering for "the absence of properly functioning civil service structure" and that "people did not think Iran and al-Qa'ida would play they role [in Iraq] that they did".

He did strike a note of contrition, saying he was wrong to suggest in a recent interview with Fern Britton that he supported regime change regardless of whether Saddam had WMDs.

The protests: ‘Lies, deceit, evasion'

Murderer, liar, war criminal, coward. Few attendees of a public hearing can have been met with such naked fury, but these were the words which greeted Tony Blair as he arrived at the Chilcot Inquiry yesterday.

As the former prime minister slipped quietly through a side entrance of the Queen Elizabeth II Conference Centre in Westminster, a crowd of 200 anti-war protesters chanted: "Blair lied, thousands died." Yesterday, their numbers diminished from the two million who marched in protest before the Iraq invasion, but they made their voices heard.

"He does not have the integrity to come and face the people. Sliding in by a back door entrance is typical of his lies, deceit and evasion," said Lindsey German, convener of the Stop The War Coalition.

Campaigners bearing placards calling for the prosecution of "Westminster War Criminals" and sporting "Jail Tony" T-shirts mingled with a fancy-dress parade of wig-clad "judges" carrying the pictures of dead Iraqi children.

But amid the circus, a sombre, dignified note was struck as campaigners solemnly read out the names of soldiers who had died in the conflict, while the families of some listened silently in the drizzle.

Inside the inquiry, families watched uncomfortably as the man they blame for their relatives' deaths spoke. One father walked out, proclaiming it was a "complete waste of time". Theresa Evans, whose 24-year-old son Llywelyn was among the first to die in the invasion in a helicopter crash, said: "I would simply like Tony Blair to look me in the eyes and say he was sorry. Instead he is in there smirking."

Others heckled Mr Blair as he finished his evidence. One of the audience shouted, "You're a liar" to which a second added, "and a murderer".

In the final twist, Grace McCann was held back by police as she attempted to perform a citizen's arrest on Mr Blair on his way out of the building. Inspired by a website, arrestblair.org [1], she insisted her actions were the only thing worthy of a "war criminal".