The head of the civil service under Tony Blair has criticised his former boss for ignoring proper Cabinet procedures in the build-up to the invasion of Iraq.
The report of the long-running inquiry into the 2003 conflict was finally published last week, with the inquiry's chairman Sir John Chilcot concluding that the Blair government had made "wholly inadequate" plans for Iraq's future following the removal of longstanding dictator Saddam Hussein.
Chilcot said key departments involved in preparation for the American-led invasion had ended up pursuing "complementary, but separate, objectives", with "untested" policy assumptions rarely challenged, and only limited discussion between key ministers of major decisions about the war.
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That view was backed by Lord Butler on Tuesday, with the former cabinet secretary – who served as the UK's most senior civil servant from 1988 to 1998 – saying Chilcot had shown a clear lack of join-up at the heart of the Blair administration.
The former civil service head, who now sits as a crossbench peer in the House of Lords, told peers in a debate on Chilcot that he had "never believed" that Blair had "lied to the British people" over Iraq, and said he accepted that the ex-prime minister was "sincere in believing that military action to remove Saddam Hussein was necessary as a last resort".
But he added: "The trouble was that he got caught in a trap in which a decision whether or not to join the Americans in military became unavoidable before other means of containing Saddam had been exhausted."
And Lord Butler said the report painted "a picture of a government which, with great respect to those who served in it, as a collective entity was dysfunctional".
"The defence and overseas policy never met in the lead-up to the war," the former cabinet secretary added. "Plans were not shared with senior ministers for fear that they would leak. The full legal reasoning of the attorney general was not made available to the cabinet. Official papers were not circulated."
Butler said the Iraq experience showed the value of "proper Cabinet procedures" being followed, and said it was vital not to view them as "pettifogging, bureaucratic impositions on busy ministers".
"They are the means inherited from successive generations of ministers and officials to ensure that the full expertise, experience and resources of government are brought to bear on crucial decisions," Butler told peers.
"That is all the more important when the decisions are about peace and war. With hindsight the Blair government's disregard for the machinery of government looks not like modernisation, but like irresponsibility."
He also sought to draw parallels between the Iraq build-up and the current crisis facing ministers and officials following Britain's historic decision to quit the European Union.
"I'm not so naive as to suppose that the interplay of personalities will not always play a part in politics as in other human affairs," he said.
"But one of the lessons of the Chilcot report is that when the great responsibility of governing the country is accepted by ministers, their main duty is good government of the people, not personal, political maneuvering.
"If government is allowed to become a game of thrones, it is the interests of the governed which will suffer. That lesson is going to be more important than ever in the difficult challenges which our government is facing today."
Butler led an earlier official inquiry into aspects of the 2003 Iraq war, and was appointed by Blair to look specifically at the intelligence used to justify the claim – later found to be inaccurate – that Hussein's regime possessed Weapons of Mass Destruction.
He told the House of Lords on Tuesday that Chilcot's report should not lead the public to conclude that intelligence was "valueless or stop us investing in it".
Rather, he said government needed to "learn the lesson" that intelligence was a "very valuable and indispensable aid to political and military judgement", rather than a "determinant" of policy.