Lord Butler, delivering his review of intelligence on weapons of mass destruction on Wednesday, looked like the amiable Oxford head of college he has become. But for all their fine chiselling, the former cabinet secretary's findings throw a harsh light on Tony Blair's conduct of government, as well as on the performance of the intelligence agencies.

In short, Lord Butler found the intelligence was generally weak, in some cases seriously flawed and, in the particular incident of the infamous 45 minute warning, plain wrong; while the government used this dubious information, ignoring the caveats and health warnings in which it was cloaked by the joint intelligence committee, to support its case against Iraq in a way that "went to the outer limits ... of the intelligence available".

In spite of Lord Butler's reluctance to condemn individuals, this was no exoneration of the prime minister. Rather, it was confirmation of a presidential style that extends well beyond foreign affairs and that allows no effective challenge to a personal mission or even obsession.

Within his self-imposed remit that restricted his review to mechanics rather than men, Butler has written a meaty analysis of the background and development of the intelligence-based case for war.

He scrupulously lays out the slowly accumulating intelligence that Osama bin Laden wanted to acquire and was prepared to use chemical, biological or even nuclear weapons.

He relates the parallel intelligence - although increasingly sparse and unreliable after Saddam Hussein evicted the weapons inspectors in 1998 - that the Iraqi president was suspected of building such weapons, and could be regarded as a potential source.

He details the impact of September 11 on the way intelligence was interpreted, even though the intelligence itself did not indicate any change in Iraqi capacity or objectives.

But he is damning about the weakness of intelligence from Iraq, the shortage of human sources, their unreliability, and, crucially, the pressure put on them and the analysts by what he calls "the urgent requirement for intelligence".

He describes a tendency to assume the worst, and to allow the worst to become the baseline. So far, so familiar, especially after last week's US Senate report. There are lessons to be learnt, and it is rather astonishing, given the criticisms in his report, that Lord Butler goes on to endorse John Scarlett as the new head of British Intelligence (MI6), and the man tasked to carry out reform.

Attention inevitably focuses on Mr Blair's determination to make political use of intelligence - and the way in which he did it - the novel and most controversial element of the run-up to the pre-emptive strike on Iraq.

The government wanted unclassified but authoritative intelligence material to advance its position. In September 2002, the JIC was charged with preparing a dossier, to lend the imprimatur of its expertize and impartiality to what was in effect a piece of advocacy for Mr Blair's position.

Although the resulting dossier, Butler found, lay just within the bounds of acceptability, and he clears the government of acting in bad faith, he cautions that it was possible to read the warning about the constraints of security as strengthening rather than weakening the material, while Mr Blair's description of it as "extensive, detailed and authoritative" may have - Butler says - "reinforced this impression".

The danger of that approach is that no one will have responsibility for putting things right. The contrast with the government's expectation that heads would roll at the BBC was marked.

The prime minister did not lie, but nor did Mr Blair tell the whole truth. He misled by omission: the great persuader, dizzied by years of deploying weapons-grade spin on the Westminster battlefield, had set an objective.

He was less discriminating in the means that he used to pursue it than standards of good governance demand - the question of trust, which has dogged him almost from the moment of his election in 1997, is back with pressing urgency.

For when Mr Blair made the case for war, we were not given the whole picture; and the part we were not given was not highly sensitive intelligence that could not be revealed, but evidence of its weakness.

We were left with the impression, reinforced in press conferences ("the threat is serious and current") and in the Commons ("I believe it is beyond doubt") that his passionate conviction that he was doing what was right was based on overwhelming evidence, when it is now clear that he was using flaky intelligence to make a risky judgment.nt.

The sofa culture revealed in evidence to the Hutton inquiry, the informal, unminuted ad hoc meetings where key decisions were taken - now defended as an unavoidable response to the 24-hour news culture - serves to exaggerate the presidential style of this government.

So does Butler's description of cabinet government where formal briefing papers for the wider cabinet are scarce, and the opportunity for informed collective debate is constrained by the habit of ministers being given information only in oral presentations that preclude detailed and thoughtful consideration.

In the end, as with Lord Hutton's inquiry into the death of the British Iraq weapons expert Dr David Kelly, the evidence unearthed by Lord Butler is more telling than his conclusions.

But Butler has laid bare a style of government that is both unaccountable and dangerous. Mr Blair sounded unapologetic in the Commons on Wednesday. We can only hope that underneath the combative veneer the true message of Butler will sink in. -Dawn/The Guardian News Service.