Tony Blair was facing the threat of legal action over his decision to take Britain to war in Iraq after a long-awaited official report delivered a damning verdict on his government's justification, planning and conduct of the military intervention in 2003.

Families of some of the 179 military personnel killed in Iraq branded the former prime minister a "terrorist", while Labour leader Jeremy Corbyn said Sir John Chilcot's long-awaited report made clear that Parliament was misled and the invasion was "an act of military aggression based on a false pretext".

Mr Blair said he took responsibility for shortcomings identified by the report and felt "more sorrow, regret and apology than you may ever know" for the grief of those whose loved ones died.

But the former prime minister said he still believed he was right to remove dictator Saddam Hussein and insisted that the inquiry's findings should "lay to rest allegations of bad faith, lies or deceit".

Unveiling his report into the UK's most controversial military engagement since the end of the Second World War, Iraq Inquiry chairman Sir John said the war "went badly wrong, with consequences to this day".

He made no judgment on whether military action was legal, but found that then attorney general Lord Goldsmith's decision that there was a legal basis for UK involvement in the US-led invasion was taken in a way which was "far from satisfactory".

Key findings in the long-delayed report included:

:: The case for war was presented with "a certainty which was not justified";

:: It was based on "flawed" intelligence about the country's supposed weapons of mass destruction (WMD) which was not challenged as it should have been;

:: The use of force to remove dictator Saddam Hussein was undertaken at a time when he posed "no imminent threat" and in a way which undermined the authority of the United Nations Security Council;

:: Planning for post-conflict Iraq was "wholly inadequate", with shortfalls in armoured vehicles to protect UK troops which "should not have been tolerated".

The report did not support claims that Mr Blair agreed a deal "signed in blood" to topple Saddam at a key meeting with George Bush at his ranch in Crawford, Texas, in 2002.

But it revealed that in July that year - eight months before Parliament approved military action - the PM committed himself in writing to backing the US president over Iraq, telling him: "I will be with you whatever."

Tearful families who gathered in London for an early sight of the 2.6 million-word report responded with fury to the details of shortcomings in planning and preparation uncovered by the seven-year inquiry.

Reg Keys said it was clear that the prime minister "deliberately misled" the country and that his military policeman son Tom "died in vain", while Roger Bacon, whose son Matthew was killed by a roadside bomb, said the families reserved the right "to call specific parties to answer for their actions in the courts".

Sarah O'Connor, whose brother Bob died when a military plane was shot down near Baghdad in 2005, branded Mr Blair "the world's worst terrorist".

The families could not be "proud" of the way the government treated their loved ones, said Mr Bacon, adding: "Never again must so many mistakes be allowed to sacrifice British lives and lead to the destruction of a country for no positive end."

In a statement summarising his findings, Sir John said: "We have concluded that the UK chose to join the invasion of Iraq before the peaceful options for disarmament had been exhausted. Military action at that time was not a last resort.

"We have also concluded that the judgments about the severity of the threat posed by Iraq's weapons of mass destruction - WMD - were presented with a certainty that was not justified.

"Despite explicit warnings, the consequences of the invasion were under-estimated. The planning and preparations for Iraq after Saddam Hussein were wholly inadequate. The Government failed to achieve its stated objectives."

The report was critical of intelligence agencies, which were working with an "ingrained belief" that Saddam retained chemical and biological warfare capabilities which he was hiding from UN inspectors and that he was determined to acquire nuclear weapons.

Joint Intelligence Committee (JIC) chairman Sir John Scarlett should have made clear to Mr Blair that suspicions about WMD had not been established "beyond doubt" prior to his publication in September 2002 of a dossier setting out the supposed threat from Saddam, the Chilcot Report found.

In a lengthy press conference in London, Mr Blair said he would never agree that those who died and were injured in Iraq "made their sacrifice in vain".

"They fought in the defining global security struggle of the 21st century against the terrorism and violence which the world over destroys lives, divides communities," he said.

"Their sacrifice should always be remembered with thanksgiving and with honour when that struggle is eventually won, as it will be."

While the Chilcot Report contained "serious criticisms", it showed that "there were no lies, Parliament and the Cabinet were not misled, there was no secret commitment to war, intelligence was not falsified and the decision was made in good faith", he said.

Announcing a two-day parliamentary debate on the report next week, Prime Minister David Cameron - who voted for war in 2003 - cautioned that the experience of Iraq should not prevent Britain from collaborating with its close ally the US in future military action.

Mr Cameron told MPs: "The decision to go to war came to decision in this House. Members on all sides who voted for military action will have to take our fair share of the responsibility.

"We cannot turn the clock back but we can ensure that lessons are learned and acted on."

In a scathing assessment of Mr Blair's actions, Mr Corbyn - who opposed war from the start - said the invasion had been judged unlawful by the "overwhelming weight of international legal opinion". But he stopped short of calling for his predecessor as Labour leader to be tried for war crimes, as some had expected.

mfl