We may not forgive him for the war, but we will make our peace with him

It was Tony Blair's war, all right. If at any point members of the Cabinet or the House of Commons had been allowed a free vote on the question, there would have been majorities for giving the UN inspectors more time. In the run-up to war, Robin Cook, then Leader of the House of Commons and Clare Short, Secretary of State for International Development, were - half-openly - opposed to military action. According to Cook's diaries, Patricia Hewitt, Secretary of State for Trade and Industry, made sceptical points when Iraq was discussed in Cabinet. At the meeting a week before the tanks rolled in, Cook told his colleagues: "We should avoid saying that we will take military action even if we fail to get a resolution." He recorded: "John Prescott nodded and I suspect that half the Cabinet agreed with me, even if no one else said so."

Gordon Brown had left it as late as the day before that gathering to declare his full and unconditional support for the Prime Minister and for military action without explicit United Nations approval. Six months earlier he had pointedly refused to say on BBC2's Newsnight whether he would support military intervention. Even Jack Straw, the Foreign Secretary, raised the possibility, at the last moment, that Britain might not join the invasion. This may have been a contingency plan in case the Attorney General's advice on international law was adverse. But John Kampfner, in his book Blair's Wars, suggests that the Prime Minister's advisers were irritated by it. Only Geoff Hoon, the Defence Secretary, has always seemed wholly signed up to the Blair line.

Ignoring the convention of collective cabinet responsibility, Blair has in any case repeatedly referred to the decision to go to war as his own. In his letter to the parents of Marc Lawrence that we publish today, he says, for example: "I did not take the decision lightly."

Because he was so personally responsible for a war that was opposed by around half the British people, its consequences for him are grave. This is not necessarily a matter of whether he was right or wrong. Even if one believes that the war was on balance justified - as I do - it has to be accepted that it was a serious political mistake. The failure to find weapons of mass destruction in Iraq, and the suspicion that the intelligence about them was over-egged, have both undermined Blair's reputation for trustworthiness. The tenacity and passion of anti-war sentiment has done to Labour's base much of what "shock and awe" did to Baghdad's infrastructure. The Labour Party itself never liked Blair much; but now there are an awful lot of members who hate him, and many more who are irrevocably disappointed with him.

The Iraq conflict has not only had a dramatic effect on Blair's standing; it has wider consequences for British foreign policy. These are quite out of proportion to the military significance of a campaign that lasted a mere 21 days, from the start of the invasion to the toppling of the statue of Saddam Hussein in the centre of Baghdad. Never again will this country be able to engage in pre-emptive military action. Blair's argument in his Sedgefield speech at the start of this month was essentially that he could not take the risk of allowing speculation about weapons falling into terrorist hands to become fact. A British prime minister would need much more robust evidence of the danger, and the imminence of it, next time.

In this, it is significant that Blair has conceded the principle that the House of Commons must give its explicit consent to the deployment of British forces. No prime minister will be able to go back on that, whatever the unwritten constitution says - or rather does not say - about Crown prerogative. The impact of the war spreads beyond Blair's domestic standing, however. The doctrine of pre-emptive action, first set out by George Bush in June 2002, has suffered a global setback.

It is worth remembering the role that Blair played in shaping domestic US opinion. He was no mere poodle; he provided President Bush with important cover in the eyes of the American public, who were wary of going it alone. It was domestic opinion polls that pushed Bush, against the unilateralist instincts of Donald Rumsfeld and Dick Cheney, to go to the United Nations. In the future, if the British are not on board it will make it that much harder for President Bush - or President Kerry - to sell military action to US voters.

The special relationship, therefore, will take some time to restore itself. Always something of a mirage, beyond the obvious commonality of two allied leaders who speak the same language, it is not obvious to most Britons what benefits they have gained from the coalition. The deep current of anti-Americanism in Britain and the rest of Europe has risen closer to the surface.

Equally damaging for Blair has been the destruction of his European ambitions. He always seemed sincere in his desire to fulfil our national destiny - his words - by persuading the British people to adopt the euro. That is surely impossible in the present climate of open hostility between Britain on the one side and the old conspiracy of Germany and France on the other.

His ambition to play a leading role in reshaping the European Union as it extends eastwards is finished. His claim to be a unifier was contradicted by his acting as chief whip for the pro-war faction against the cheese-eating and beer-swilling surrender monkeys last year. They will not forget that it was he who organised an open letter with eight "New European" signatories in January last year. Not only that, but his attempt to push the UN towards a new doctrine of humanitarian intervention, building on the consensus over Kosovo, has been set back. The confusion between intervening to avert humanitarian catastrophe and to avert a putative terrorist threat has poisoned support for the first kind of action.

The damage to Blair is serious, then. Its effects are particularly concentrated and corrosive among two important groups. One is the Labour Party, which is bad enough; the other - far more importantly - is the media. My impression is that journalists are more likely to be anti-war than the average member of the public. Less ideologically, they (we) are also beginning to find Blair boring, and want to move on to the next new thing.

Opinion polls, however, suggest that the wider public is willing to give Blair more time, but not without first giving him an admonitory drubbing in local and European elections in June. In this, I think their instincts are sound. Given that the "stop the war" tendency got its wish only a little less than one year ago, British voters are more interested in who can deliver better public services. Forced to choose between Michael Howard and Gordon Brown, I think most people would take the third way and stick with Tony Blair.