Be clear what Lord Butler is saying: Britain went to war on a false premise

Do not be deceived by the predictably mild tone. Lord Butler's report is no whitewash. It may not contain a killer sentence, but it comes surprisingly close to delivering one.

After highlighting the discrepancies between the original intelligence and the way it was presented, Butler concludes: "More weight was placed on the intelligence than it could bear".

Think about that seemingly modest sentence. The intelligence was the basis for Tony Blair's decision to go to war. He presented it with a passionate and alarming conviction. Consider also Mr Blair's response in the Commons. For the first time he accepted that the intelligence was "less certain and less well grounded than was stated at the time". Presumably he means that the intelligence was more speculative and tentative than he stated at the time. This is a devastating confirmation from an inquiry, and by implication from the Prime Minister, that the qualifications and caveats that came with the intelligence were omitted from the public presentation. Such a confirmation would be fairly damaging if the issues were relatively trivial. Instead, Lord Butler was investigating the origins of a war.

What is more, he was functioning within a limited remit in which he was obliged to focus on the intelligence rather than the culpability of political leaders. It was Mr Blair who set the remit, no doubt aware that Lord Butler was not the type to stray beyond a brief. Lord Butler evidently tried not to do so.

Even so, the gathering of the intelligence and the political context became so intertwined that Lord Butler could not avoid making implicit judgements on the Prime Minister. He concludes that Mr Blair may have given the impression that the intelligence was "firmer" than it was. He decides that the intelligence was "seriously flawed" and, more significantly as far as Mr Blair is concerned, "open to doubt". Mr Blair expressed no doubts, at least in public. The report confirms that recent intelligence was "limited". The report also criticises the "informal" arrangements in Downing Street in the build up to the September dossier on Saddam's WMD.

The familiarity of these charges, and Lord Butler's reluctance to criticise individuals, should not detract from their significance. They point to a single conclusion: Britain went to war on a premise that turned out to be false.

In the Commons Mr Blair clung to Lord Butler's judgement that he had acted in good faith. Lord Butler explained at his press conference that Mr Blair must have believed in all his alarming assertions because he must have known that truth would be discovered after the war. There is some logic in this hypothesis although Lord Butler underestimates the political pressure Mr Blair was under when he paraded the intelligence without any caveats or qualifications. The Prime Minister had told President George Bush long before that Britain would take part in the war. As the conflict approached he found that most of the voters did not support him. Mr Blair faced the prospect of letting down the most powerful leader in the world or persuading voters and some of his own MPs to change their minds. In choosing the latter course he needed all the ammunition he could get.

The limits of Lord Butler's remit mean that we have to read between the lines, but it does not take a genius to do so. Mr Blair is a political leader who never knowingly understates a case. He decides on a message, refines it, sharpens it and then hypes it up. His cautious, incremental 1997 election manifesto became a programme to create a New Britain, a country that would be young again. His vague ideas for social security became a "welfare revolution". He predicted that Ken Livingstone would be a "disaster" for London. He declared that he possessed "no reverse gear". In such a political leader it is easy to see how "sporadic and patchy" intelligence became proof that Saddam possessed WMD. As Ken Clarke argued in the Commons yesterday, Mr Blair would not have won the pivotal vote in advance of the war if MPs had been presented with the qualifications that accompanied the intelligence.

Other familiar characteristics in Mr Blair's political personality also came into play. He often makes premature commitments that he subsequently cannot meet. The late Lord Jenkins was promised a referendum on electoral reform. Pro-Europeans in this country and abroad were told that a referendum on the single currency would be held in this term. For good reasons Mr Blair decided that he could not deliver.

There is some evidence that he told President Bush at their Crawford summit, a year before the war, that he would support the invasion. He could not get out of this pledge and had to find a way of meeting it. He had made a commitment to a president as if he were a president too.

There is also a hugely underestimated factor in analysing the Blair premiership: he has never held any other post in government apart from that of Prime Minister. His "informal" style, the lack of cabinet consultation, is based on how he functioned as the most successful leader of opposition in post- war British politics. He has no other model on which to run a government.

His lack of ministerial experience also partly explains why he chose to believe the intelligence with such unquestioning passion. He has never been a home secretary or foreign secretary, handling intelligence and observing a prime minister assessing intelligence with scepticism. As Lord Butler asserts, there is a lot of evidence to suggest that Mr Blair believed this patchy and limited intelligence.

Michael Howard gave his most effective performance in the Commons yesterday afternoon, short and forensic. Wisely he raised only two key points, the discrepancy between the original intelligence and the way it was presented and the broader question: Would Mr Blair be trusted again in a similar situation? But Mr Howard has only a tiny amount of political space in which to mount an attack.

In response, Mr Blair resorted to the old argument that the Conservative leader had supported the war and therefore was being opportunistic. This was one of Mr Blair's calculations from the beginning: he would get away with this because he would have the support of most Conservative MPs. The Conservative leadership walked into a trap by giving unqualified support in advance of the war.

But Mr Howard's unanswered question remains at the heart of the current political situation and has a wider application. Will Mr Blair be trusted again? When he makes sweeping claims in a referendum on Europe, will voters believe him or will they recall how he chose to present the intelligence in advance of war? When he asserts with good cause that public services are improving, will voters wonder whether he is going over the top again, that more weight is being placed on the evidence than the evidence can bear? In the Commons yesterday afternoon Mr Blair stated that he accepted responsibility for the mistakes that were made. Even in apparent contrition he was being evasive. What did he mean by taking responsibility for the mistakes? There is not a killer blow in this report, but Lord Butler has wounded without naming his victims.