The assault on Iraq which began yesterday is a war the British people do not want. Never before, at least since public opinion first became a serious political consideration, has this country gone to war with only a minority of the population in support.
Tens of thousands across the country drove that point home yesterday, in the biggest ever display of coordinated civil disobedience on the streets of our towns and cities. Many more will march for peace in London tomorrow. Tony Blair's appeal for national support for the war effort is already falling on deaf ears.
Despite the government's efforts over the past few days to re-spin the attack on Iraq as if it were now supported by a new national consensus, the anti-war movement - unprecedented in its scope and representativeness - is clear: we cannot and will not support this war.
The logic is simple. If it is right to oppose a crime when it is being publicly contemplated, how much more important is it to do so when it is in the process of commission. It is not those who oppose the war who need to justify themselves, but those Labour MPs who assured their local parties as recently as last weekend that they would never support war without UN authority, only to do just that days later.
Ministers will, of course, play on the sympathy of many people for British troops. Yet the fact remains that they are not fighting in the interests of the British people, nor on behalf of any international community, but for a reactionary and dangerous US administration to which Tony Blair has subordinated our country.
The prime minister was, however, clearly right when he told the Commons this week that the conduct of this crisis will shape world politics for the next 20 years. For him, that apparently means a generation in which international affairs will be conducted on the basis of a disregard for law and UN authority, and an unconditional subordination to US imperial power.
That outlook is not shared by the other major powers, France, Russia, China and Germany among them. The great majority of the countries of the world appear no more ready to embrace the hegemony of the US today than they did that of the British empire a century ago.
The most sobering aspect of the great power split provoked by George Bush's unilateralism is the reminder that, in the past, neo-colonial conflicts like this one have often led to much larger wars. So now is the time to speak out, or risk becoming complicit in a repetition of some of the worst crimes of the 19th and 20th centuries.
Blair's responsibility for this crisis cannot be concealed by the week's big lie - that it is all the fault of the French. The prime minister did not get the second security council resolution which he so craved because the majority of the council opposed him and the US administration was not interested anyway.
It is far more likely that, had Britain adopted the firm position of France and Germany from the beginning, a peaceful solution to the crisis could have been found. Instead, he has given comfort to the wild men in charge in Washington throughout by denying them the total international isolation their policies warrant.
As it is, it is the prime minister himself who is isolated. His war is opposed by most of the people he was elected to represent, and denounced by virtually every expert on international law except the attorney general, as well as by almost every other country he would like to claim as a friend.
The course of events in the Gulf itself is unpredictable. Blair is banking on a sense of fatalism and powerlessness to immobilize the majority opposed to the aggression; but he knows he has no margin for error in either military or political events as they unfold. Beyond the coalition of Conservatives and the minority of Labour backbenchers supporting the invasion, public opinion is unlikely to tolerate either British military casualties or Iraqi civilian casualties on any significant scale, given that it was never convinced of the case for war in the first place.
It should have been possible to avoid the possibility of either. But Tony Blair has chosen loyalty to the US president over the people of this country. As a result, tomorrow will see the largest-ever demonstration against a war in which British troops are fighting, while they are doing so. That is the pass to which Tony Blair has brought the country, even before the British people start to reap the inevitable whirlwind the prime minister is sowing in the Middle East. This is a day of shame for Britain. Only the actions of ordinary people standing up for peace and democracy can now redeem it.
Andrew Murray is chairman of the Stop the War Coalition, which has called tomorrow's demonstration in London