The scathing Chilcot report detailing catastrophic mistakes and failures by former UK Prime Minister Tony Blair and his government on the Iraq war singles out the intelligence community for particular criticism.
The official report, released on Wednesday, into the UK's involvement in the war which began in 2003 said the invasion was not the last resort action presented to MPs and the public, there was no imminent threat from Saddam Hussein and the intelligence case was not justified.
The seven-year inquiry also suggests Mr Blair ran his government in a way that meant the possible and probable consequences of military action in Iraq were never properly considered.
Many had predicted the report would be a 'Whitehall whitewash" but this was a tougher, more damning report than had been feared, said BBC security correspondent Frank Gardner.
"It's very clear that catastrophic mistakes and failures were carried out."
One of the most important was the intelligence failure.
In September 2002, Britain's secret intelligence service MI6 distributed to senior British officials the reports it had received from its sources, alleging that Iraq had "accelerated the production of chemical and biological agents".
"MI6 ... reckoned that they had an agent on the inside in Iraq, somebody who had first hand knowledge of the alleged biological and chemical weapons - and he was peddling a load of lies," said Mr Gardner.
"This intelligence got fed up the chain, it was never properly assessed, and Sir John Chilcot in his report is damning of this - both of the fact that the intelligence was wrong, that it was wrongly assessed, and that decisions were taken by the same people who were doing the assessment of it.
"That is one of the key lessons here, that never again should Britain, or any other country for that matter, take a decision to go to war based on faulty intelligence.
The military were unprepared, there was a rush into war, and an underestimation of the risks involved and of the "complete shambles that Iraq was going to be post-invasion".
No weapons of mass destruction were ever found in Iraq. By September 2004, SIS withdrew additional key intelligence reports used by British and American leaders to justify the invasion.
Was there intention to mislead?
The report cleared Downing Street of one of the most controversial charges of all, that Number 10 deliberately manipulated or "sexed up" the case.
"There is no evidence that intelligence was improperly included in the dossier or that Number 10 improperly influenced the text," it said.
But according to BBC political editor Laura Kuenssberg, even if there was no evidence of deliberate intent to mislead, "politics blurred the practical judgements".
"The impression is certainly created that Tony Blair's government was looking for facts to support his determination to change the Iraqi regime, rather than looking at the facts carefully in order to make that decision," she said.
Facing reporters after the release of the inquiry findings, Mr Blair insisted he did not mislead the country. "There were no lies, there was no deceit, there was no deception," he said.
However former British Labour cabinet minister Clare Short said the report makes it clear Mr Blair misled the cabinet, the British parliament and the public.
Ms Short, who resigned as a minister in protest, told Nine to Noon the report shows Mr Blair was not straight with the British people nor his colleagues.
"There was exaggeration, manipulation, not being straight.
"And then he said this was one of the most difficult decisions he's ever made.
"Well yes. And it was a wrong decision too.
"And then he says but it was absobutely right and Saddam Hussein couldn't be allowed to remain there. But the Chilcot report said Saddam Hussein was contained, there wasn't any threat from WMD [weapons of mass destruction].
Legal or not?
The US-led invasion was preceded by a long period of diplomacy in which Britain led and failed in efforts to secure explicit United Nations authorisation for military action.
This has given rise to a long and heated debate about whether the war was lawful or not, a debate that is likely to continue despite the inquiry findings.
The Chilcot inquiry was not set up to make any legal findings and its report pointed out the committee was not a court nor a jury.
Within that limitation, though, the committee said: "We have, however, concluded that the circumstances in which it was decided that there was a legal basis for UK military action were far from satisfactory."
The report also reveals that the final decision on legality was taken by Mr Blair, not the Cabinet or the government's legal officers. His Attorney General made that plain in documents that the inquiry has published, saying, "this is a judgement for the prime minister".
The specific decision was as to whether Iraq was in material breach of UN resolution 1441, so that military action could be legally justified without a further resolution.
Correspondence from Mr Blair's office replies to say "it is indeed the prime minister's unequivocal view that Iraq is in further breach". But Chilcot concludes "It is unclear what specific grounds Mr Blair relied upon in reaching his view."
- RNZ / BBC / Reuters