The long-awaited official report into Britain's involvement in the Iraq War has delivered a scathing verdict on UK government ministers' justification, planning and conduct of a military intervention which "went badly wrong, with consequences to this day".
The inquiry panel agreed unanimously that, while military action in Iraq "might have been necessary at some point", at the time the invasion was launched, there was "no imminent threat from Saddam Hussein", "the strategy of containment could have been adapted and continued for some time" and "the majority of the Security Council supported continuing UN inspections and monitoring".
Former British prime minister Tony Blair presented the case for war in 2003 with "a certainty which was not justified" based on "flawed" intelligence about the country's supposed weapons of mass destruction (WMD) which was not challenged as it should have been, found report author John Chilcot.
Unveiling his 2.6 million-word report into the UK's most controversial military engagement since the end of the Second World War, Chilcot 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."
Chilcot said Mr Blair was wrong to claim that the risks of instability following the invasion could not have been known in advance.
Although he made no judgment on whether military action was legal, Chilcot's seven-year inquiry found that UK 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".
The report does not support the claims of Blair critics that the former UK prime minister agreed a deal "signed in blood" to topple Iraqi dictator Saddam Hussein when he met George Bush at his ranch in Crawford, Texas, in April 2002.
But it reveals that in July that year - eight months before UK Parliament approved military action - Mr Blair committed himself in writing to backing the US President over Iraq, telling him: "I will be with you whatever."
The report found that the use of force to remove Saddam 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.
The risks of a hastily-prepared military mission to invade and occupy four provinces of southern Iraq were not properly identified, leading to shortfalls in key equipment such as helicopters and surveillance gear.
Britain’s ministry of defence was "slow" to respond to the threat from insurgents' roadside bombs, resulting in delays in the supply of armoured vehicles to protect troops which "should not have been tolerated".
And the Blair Government's "wholly inadequate" preparations for the aftermath of war "failed to take account of the magnitude of the task of stabilising, administering and reconstructing Iraq".
Mr Blair himself over-estimated his ability to influence US policy at a time when ministers were aware of the "inadequacy" of Washington's plans.
The report acknowledged that the initial campaign to overthrow Saddam was successful and praised the "great courage" of service personnel and civilians involved during and after the invasion, which led to the deaths of more than 200 UK nationals and at least 150,000 Iraqis.
But it found that Britain's military role "ended a very long way from success" and it was "humiliating" that the UK was reduced to doing deals with a local militia group in Basra, releasing captured militants in return for an end to attacks on British forces.
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.
The UK’s Joint Intelligence Committee (JIC) should have made clear to Mr Blair that its 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, Chilcot found.
As late as March 17 2003 - three days before the invasion began - JIC chairman John Scarlett continued to advise the PM that Iraq possessed chemical and biological weapons and the means to deploy them.
But Chilcot said: "It is now clear that policy on Iraq was made on the basis of flawed intelligence and assessments. They were not challenged, and they should have been."
The findings of the 2004 Iraq Survey Group into Iraq's WMD capabilities were "significant" but did not support pre-invasion statements by Mr Blair and then foreign secretary Jack Straw, which warned of vast stocks of weapons and an urgent and growing threat.
Mr Blair's response that Saddam retained "the intent and the capability" to develop and use WMD did not match the justification for military action given before the conflict, said Chilcot.
The report found that Mr Blair urged Mr Bush in the immediate aftermath of the September 11 terror attacks in 2001 not to take "hasty" action against Iraq.
But it said by the time of the Crawford meeting, there had been a "profound change" in his thinking, with the UK government stating openly that Iraq was a threat that had to be dealt with, and the JIC privately concluding that Saddam could not be removed without an invasion.
The British government's insistence that Iraq must disarm or be disarmed implied the readiness to use force if Baghdad did not comply, and contingency planning for an invasion had indeed begun, the report found.
In his July 28 letter, Mr Blair told Mr Bush that a coalition for military action would be dependent on the authority of the UN, and a resolution was passed by the Security Council in November 2002 giving Iraq a final opportunity to disarm to avert war.
But Chilcot found that by December, Mr Bush had decided military action would take place anyway in early 2003 - a timetable which Mr Blair accepted at the end of January.
Although Mr Blair and Mr Straw subsequently blamed France for the failure to secure a resolution backing war and claimed to be acting to uphold the authority of the Security Council, the report found that "in the absence of a majority in support of military action, we consider that the UK was in fact undermining the Security Council's authority".
The circumstances under which Lord Goldsmith provided a legal justification for UK involvement were "far from satisfactory", the report found.
Having initially advised Mr Blair in January 2003 that a second UN resolution was necessary, he later produced written advice that there was a "reasonable case" that the November resolution alone was sufficient.
On March 14, he asked Mr Blair to confirm that Iraq had breached the terms of the first resolution, which required Baghdad to provide access to UN weapons inspectors.
The precise basis on which Mr Blair gave that crucial confirmation "is not clear", said the report, which added that the issue should have been discussed by Britain’s cabinet.
The report dismissed Mr Blair's argument that the emergence following Saddam's fall of a violent insurgency against occupying allied forces could not have been foreseen.
"We do not agree that hindsight is required," stated Chilcot. "The risks of internal strife in Iraq, active Iranian pursuit of its interests, regional instability and al Qaida activity in Iraq were each explicitly identified before the invasion."
Mr Blair "did not establish clear ministerial oversight of UK planning and preparation, he did not ensure that there was a flexible, realistic and fully-resourced plan that integrated UK military and civilian contributions and addressed the known risks".
Chilcot acknowledged the "deep anguish" of the families of those killed and injured in Iraq, many of whom were present in London to read his report for themselves.
And he said the people of Iraq had "suffered greatly" from the failure to deliver on the vision of a peaceful, secure and democratic Iraq set out by the US and its allies in the eve-of-war summit in the Azores. At least 150,000 and probably many more had died, and one million had been forced from their homes.
The UK took responsibility for south-eastern Iraq without a formal ministerial decision and "without ensuring that it had the necessary military and civilian capabilities to discharge its obligations, including, crucially, to provide security", found Chilcot.
"The scale of the UK effort in post-conflict Iraq never matched the scale of the challenge. Whitehall departments and their ministers failed to put collective weight behind the task. In practice, the UK's most consistent strategic objective in relation to Iraq was to reduce the level of its deployed forces."
The MoD was slow in responding to the threat from improvised explosive devices (IEDs) used by insurgents to inflict multiple casualties on occupying forces.
And from 2006, when UK troops were deployed in the Helmand province of Afghanistan, the armed forces were conducting two campaigns without "sufficient resources" to do so.
Decisions on resources for Iraq were affected by the demands of the operation in Afghanistan, with a "material impact" on the availability of essential kit like helicopters and surveillance equipment.