So what would have happened if Britain had opposed the war?

The debate in Britain about the war against Iraq is becoming absurdly parochial. It's reminding me of a long and silly Monty Python sketch. A visitor from Mars might easily assume that the key players in the build-up to war were Greg Dyke, Andrew Gilligan and Dr David Kelly. The same visitor might be equally bewildered to discover that the political classes are nervously awaiting Lord Hutton's verdict on the war, when the judge's real remit is to find out the circumstances leading to a single tragic death in Oxfordshire, which is some distance away from Baghdad.

The parochialism extends to more substantial issues. Last week's report from the Intelligence and Security Committee of MPs revealed that Tony Blair received intelligence suggesting that the war against Iraq risked heightening the terrorist threat. Some opponents of the war claimed that here was the evidence that proved he should have called the whole thing off. They spoke as if this was the only intelligence he was receiving and, much more importantly, that he was in a position to actually apply the brakes.

As the debate in this country becomes more narrowly focused, we are in danger of forgetting the obvious: that it was the US pulling the strings, and that it was only the US administration that could have done that. As a result of the various inquiries and books on the subject, it is becoming increasingly clear that Blair took a single key decision. He resolved to back President Bush in his determination to remove Saddam, in the same way that he had supported President Clinton in all his military adventures. The alliance with the US was the first consideration, while the precise merits of attacking Iraq were secondary. If Bush had targeted a tyrant other than Saddam, Blair would almost certainly have been with him. Once the Prime Minister had taken that decision, it was inevitable that he would never again be fully in control of events. How could he be in control with so many others involved, not least the unpredictable and divided US administration?

A combination of the Hutton inquiry, the report from the intelligence committee, and Peter Stothard's account of the build-up to war - 30 Days: A Month at the Heart of Blair's War - reveal the calculations being made in No 10. There was an absolute conviction that the alliance with the US was necessary, and that the war was justified. There were some doubts about the intelligence. According to evidence provided to the inquiry, Blair's chief of staff, Jonathan Powell, expressed concerns about whether the intelligence justified claims that Iraq was an imminent threat. Last week's committee report went further by revealing that some of the intelligence highlighted the risks of war.

But, by this stage, Blair had almost certainly assured Bush that Britain would support the US in a war against Iraq. Almost a year before the conflict, he stated after a summit with Bush: "Saddam's weapons of mass destruction must be dealt with. There is no doubt about that. The only question is how." It is inconceivable that the military option was not discussed between the two leaders at that point. Stothard's book - much more revealing than the reviews have suggested - highlighted Blair's broader calculations. At one point the author listed authoritatively the reasons why Blair went to war. They included: "Gulf War 2 - President George W Bush vs Saddam - would happen what anyone else said or did ... It would be more damaging to long-term world peace and security if the Americans alone defeated Saddam than if they had international support to do so."

For a variety of complex reasons Blair was not going to break with the US over Iraq. These included his determination - from the moment President Bush was elected - to show that a Labour prime minister could work with a Republican president, without yielding any political space to the Conservatives. More substantial was the argument that engaging with the US administration would be more constructive than turning away from it, and thereby reinforcing its isolationism. Clinton was one of those making this argument to Blair. Part of the political trap that the Prime Minister fell into was that he was never able to make this case in public: "It would be a lot worse if we let some of those maniacs get on with it on their own..." For diplomatic reasons he was only able to deploy the argument about Saddam's weapons, which left him exposed when they did not turn up.

Opponents of the war - including this column and this newspaper - can have easy hits, claiming vindication. The weapons have not been found. The political and military situation in Iraq is as unstable as we predicted it would be. But we face a question that is difficult to answer: what would have happened if Britain had joined France in vehement opposition to the US? The war would still have gone ahead; the Bush administration would have been confirmed in its defiant insularity; and there would not have been even a modest attempt to restart the Middle East peace process.

There are more serious issues arising from the war than the perverse emphasis on the way the Government presented a dossier. It was not sexed up, as the BBC alleged. It was much more serious than that: the dossier accurately presented inaccurate intelligence. The quality of intelligence on Iraq was poor. We need to know why, not least because intelligence will play an increasingly important role in justifying future military interventions. The US is hopeless at policing countries after a war. It lost interest in Afghanistan, and is provoking even more chaos now.

Meanwhile, the leading countries in the European Union need to have a clearer sense of how they address a new world order with a single superpower, one that is getting mightier by the day and finds itself in a position to do more or less what it likes. The whole premise of Blair's foreign policy, in which he envisaged Britain being the bridgehead between Europe and the US, has collapsed over Iraq. But we should not forget that President Chirac's opposition to the war didn't prevent it from happening. The US was in a position to ignore the opposition of France, Germany, Russia and most of the UN. It is so strong militarily that it would also have been in a position to cast aside the objections of a British government.

This does not justify the war, or the decision by Britain to back the US. The case for war was not convincing enough; and, in an unexpected way, the plethora of inquiries are exposing how the Government went to great lengths to make it convincing. As I argued last week, a decent and progressive government lost an entire year as a result of the conflict. It now appears to be in danger of losing another 12 months trying to justify what happened.