LONDON — Prime Minister Tony Blair of Britain went to war alongside the United States in Iraq in 2003 on the basis of flawed intelligence that went unchallenged, a shaky legal rationale, inadequate preparation and exaggerated public statements, an independent inquiry into the war concluded in a report published on Wednesday.
The long-awaited report by the Iraq Inquiry Committee, led by a retired civil servant, John Chilcot, takes up 12 volumes covering 2.6 million words, four times longer than “War and Peace,” and took seven years to complete, longer than Britain’s combat operations in Iraq. It concluded that Mr. Blair and the British government underestimated the difficulties and consequences of the war and overestimated the influence he would have over President George W. Bush.
The result amounts to a broad indictment of Britain’s involvement in the Iraq war that overthrew Saddam Hussein and its aftermath, and it portrays Mr. Blair as trying without success to restrain Mr. Bush, to push him to obtain full United Nations Security Council authorization and to warn about the difficulties of the war — and deciding to go to war alongside Washington nonetheless.
Judging that Britain should stand by the United States, Mr. Blair told Mr. Bush in a private note as early as July 28, 2002, “I will be with you, whatever.” Mr. Blair knew by January 2003 that Washington had decided to go to war to overthrow Mr. Hussein and accepted the American timetable for the military action by mid-March, pushing only for a second Security Council resolution that never came, “undermining the Security Council’s authority,” the report concludes.
The report is likely to underline in Britain the sense that Mr. Blair was “Washington’s poodle,” the phrase widely used by Mr. Blair’s critics at the time. The report says the lessons from the British government’s conduct are that “all aspects” of military intervention “need to be calculated, debated and challenged with the utmost rigor,” and decisions, once made, “need to be implemented fully.”
Mr. Chilcot, speaking for the inquiry as a whole, concluded that “sadly, neither was the case in relation to the U.K. government’s actions in Iraq.” And he emphasized that Britain’s relationship with the United States was strong enough “to bear the weight of honest disagreement.”
“It does not require unconditional support where our interests or judgments differ,” he continued.
The inquiry, while revealing little that changes the understanding of the war, its preparation and aftermath, pulls no punches on a deeply flawed British governmental process.
“It is now clear that policy on Iraq was made on the basis of flawed intelligence and assessments,” Mr. Chilcot said. “They were not challenged, and they should have been.”
The report says: “At no stage was the hypothesis that Iraq might not have chemical, biological ornuclear weapons or programs identified and examined” by the Joint Intelligence Committee.
“The assessed intelligence had not established beyond doubt either that Saddam Hussein had continued to produce chemical and biological weapons or that efforts to develop nuclear weapons continued,” the report said.
“The J.I.C. should have made that clear to Mr. Blair,” who spoke of Mr. Hussein’s possessing “vast stocks” of weapons of mass destruction when there was no definitive evidence to support them, according to the report.
“The U.K. chose to join the invasion of Iraq before the peaceful options for disarmament had been exhausted,” the report said. “Military action at that time was not a last resort.”
In the end, the British government “failed to achieve its stated objectives,” the inquiry concluded, and said that “Mr. Blair overestimated his ability to influence U.S. decisions on Iraq.”
Mr. Blair was said to have been advised by his diplomats and ministers of “the inadequacy of U.S. plans” and their concern “about the inability to exert significant influence on U.S. planning.” But he chose to override their objections.
The inquiry concluded, bluntly: “Mr. Blair eventually succeeded only in the narrow goal of securing President Bush’s agreement that there should be U.N. authorization of the post-conflict role.”
Influence, it said, “should not be set as an objective in itself.”
“The exercise of influence is a means to an end,” it said.
The inquiry did not make any judgment on legal culpability. Outside the convention center where Mr. Chilcot spoke, near Parliament, demonstrators chanted and held up a sign reading: “Blair Must Face War Crimes Trial.”
In a statement issued later on Wednesday, Mr. Blair said that he took “full responsibility for any mistakes, without exception or excuse,” but he emphasized that he had not been accused of falsifying intelligence or misleading his cabinet colleagues, and that he had made no “secret commitment to war.”
Mr. Blair had previously said that he had no regrets about acting to remove Mr. Hussein from power. He has denied inventing or distorting intelligence, but he accepts that there were flaws in the intelligence process, and he says that he now understands more about the complications of the Middle East. Once the report was published, he said in May, he looked forward to participating in “a full debate” on the issues.
But the inquiry is quietly scathing. “The judgments about the severity of the threat posed by Iraq’s weapons of mass destruction were presented with a certainty that was not justified,” it said.
The current leader of the Labour Party, Jeremy Corbyn, has called the war illegal.
The verdict of the inquiry into the planning and conduct of British military involvement in Iraq was withering, rejecting Mr. Blair’s contention that the difficulties encountered after the invasion could not have been foreseen.
“We do not agree that hindsight is required,” Mr. Chilcot said. “The risks of internal strife in Iraq, active Iranian pursuit of its interests, regional instability and Al Qaeda activity in Iraq were each explicitly identified before the invasion.”
Over all, Mr. Chilcot continued, “the government’s preparations failed to take account of the magnitude of the task of stabilizing, administering and reconstructing Iraq, and of the responsibilities which were likely to fall to the U.K.”
With the military also conducting operations in Afghanistan, resources were stretched, having an impact on the availability of helicopters and surveillance equipment.
Britain’s Defense Ministry was slow to respond to the threat from improvised explosive devices, and there were unacceptable delays in providing properly protected patrol vehicles, the report said.
By 2007, the British were forced to do deals with militia in the southern city of Basra, releasing detainees in exchange for an end to targeting of its forces.
“It was humiliating that the U.K. reached a position in which an agreement with a militia group which had been actively targeting U.K. forces was considered the best option available,” Mr. Chilcot said.
Mr. Blair is blamed directly for many failings. “Despite concerns about the state of U.S. planning, he did not make an agreement on a satisfactory post-conflict plan a condition of U.K. participation in military action,” the document said. “The U.K. was fully implicated” in the decisions of the postwar Coalition Provisional Authority, “but struggled to have a decisive effect on its policies.”
The cabinet did not discuss military options or their implications. At the same time, a laudable, “can do” attitude among the military meant that “at times in Iraq, the bearers of bad tidings were not heard.”
The war killed about 200 Britons, including 179 British troops, almost 4,500 American personnel and more than 100,000 Iraqis.
The Iraq Inquiry held public hearings from 2009 to 2011, taking evidence from more than 150 witnesses and analyzing 150,000 documents. The release of the report was repeatedly delayed, in part by disagreements over the inclusion of classified material, including conversations between Mr. Blair and Mr. Bush, whose communications with Mr. Blair were not released by the United States, and in part because individuals set to be criticized were allowed to read drafts of the report and respond to them before a final version was written.
Sarah Helm, the wife of Mr. Blair’s then chief of staff, Jonathan Powell,wrote on Monday about a Blair-Bush phone conversation she overheard in early March 2003, about which she took notes. In a discussion about a second Security Council resolution, Mr. Bush was described as jokey and bluff, praising Mr. Blair for his “true courage,” while Mr. Blair emphasized that “we’ve got to make people understand we are not going to war because we want to but because there is no alternative.”
Mr. Bush said: “You know, Tony, the American people will never forget what you are doing. And people say to me, you know, is Prime Minister Blair really with you all the way? Do you have faith in him? And I say: ‘Yes, because I recognize leadership when I see it. And true courage. He won’t let us down.’ ”
Mr. Blair laughed, unsure, Ms. Helm recounted, then said, “Well, it might be my epitaph.”