So that’s it then. We’re pulling out of Iraq within the next, ooh, 18 months or so, before we become a “provocation”. So said the prime minister last week, echoing the dramatic change of tone from the White House.

Funny, but it seems only yesterday that Tony Blair was castigating advocates of withdrawal as disloyal defeatists and appeasers of terrorism. Now we are handing large areas of Iraq, like Amarah, over to people like Moqtada al-Sadr, one of the blackest terrorists in the Middle East.

Of course we won’t cut and run. We’ll stay the course, protect democracy and all that. But first of all, we’ll get the hell out of there as soon as humanly possible. Seems that the prime minister really did agree with the head of the army, Sir Richard Dannatt. The morale and integrity of the British armed forces are being seriously undermined.

But the real impetus for the ‘troops out’ movement is coming from conservatives in the US. The Republican grandee James Baker, the former secretary of state and member of the George Bush Snr clan, has called for withdrawal in an as yet unpublished report of the cross-party Iraq Study Group which calls for a new strategy, ie we’re stuffed.

Now, there may be an element of electoral gamesmanship about the leaks of his report. With the November congressional elections imminent, and the war profoundly unpopular, it doesn’t do the Republican Party any harm for it to appear as if there is an end in sight to the flow of body bags.

However, even discounting for electoral opportunism, there is still something astonishing about a prominent Republican calling effectively for America, formerly the greatest military force in history, to recognise that it has been decisively defeated by a handful of ragheads with kalashnikovs.

If America and Britain leave Iraq before democracy is established and the insurgency destroyed, then this will indeed be a comprehensive defeat of US war aims. Baker even contemplates inviting Iran and Syria to take over as guarantors of the new Iraqi state. This is beyond irony. For members of the “axis of evil” to be offered Iraq on a plate is surely as great a defeat for American policy in the Middle East as it is possible to contemplate – short of releasing Saddam Hussein and restoring the Ba’ath Party to power.

The Iraq invasion was supposed to stand as a warning to America’s enemies of the penalties of not accepting the Pax Americana. It has done exactly the reverse.

But this really won’t do. Britain and America cannot just walk away as if nothing has happened, or as if it really has nothing to do with us. “Well, we’ve done our best, but you just can’t stop these people killing each other, can you?”

The way Western leaders are talking you would think that the war in Iraq had been started by the Iraqis themselves. That we just tried to act as peacemakers, and to halt the bloodshed, as Nato forces did in Bosnia.

But this is a war that we are solely responsible for. A half-million or so Iraqis would still be alive had we not marched in three years ago. The insurgency is our creation. And if Iraq collapses into civil war then we will have been responsible for it and for the probable disintegration of the state.

Don’t get me wrong. I want to see the troops out of Iraq as soon as possible. This column has consistently argued that the longer we stay the worse the violence will become. There is no solution to the crisis that doesn’t involve the removal of American troops from Iraq.

They are a magnet for every jihadist and mujahideen in the Muslim world. Only when they are out of the picture can this ravaged land start the long and probably bloody process of reconstruction.

Britain and American made the stupendous error of believing that Christian troops would be welcomed as liberators by a Muslem country. But they cannot say they weren’t warned. What has happened in Iraq is precisely what this column, along with numerous critics of the war, said would happen.

It didn’t take a genius to work it out. And, of course, we now know the intelligence services on both sides of the Atlantic were saying the same thing: an invasion by Israel’s principal ally and benefactor would inflame the region.

But this is not just water under the bridge. We cannot just move on. There can be no closure on this hideous chapter in relations with the Muslim world until there is some kind of a reckoning.

A greater war crime is difficult to imagine than invading a country that posed no threat and then destroying it. Until those responsible are forced to recognise their culpability and are held to account, this matter cannot rest.

The most obvious way is for this to be done by the electorates in America and Britain. But democratic accountability is not easy when neither of the principle architects of the disaster – Blair and Bush – are seeking re-election.

There is then, of course, the judgement of history. The PM and the president will go down as two of the worst leaders in modern history, and the greatest threats to world peace since Slobodan Milosevic. It is likely that a new and dangerous round of nuclear proliferation will be one of the unintended consequences of Iraq .

Clearly, America is going to emerge very much weaker from the Iraq war, much as Britain lost world influence after Suez. American military might has been exposed as a paper tiger, unable to enforce its will on a backward country in the Middle East. The rising powers in the East – China and India – will draw the obvious conclusion that there is a geopolitical vacuum emerging in international affairs. One which they, perhaps, with 40% of the world’s population and most of its industry, can seek to fill.

This is a stupendous chargesheet against Blair and Bush and that is before we address the question of the formal legality of the war. There is a strong prima facie case that, by invading a sovereign country that posed no military threat, Britain and America breached international law. If this were Bosnia, we would be arraigning Bush and Blair with war crimes. Who knows, it may come to that. Once these men are out of office, and lose their powers of patronage and their constitutional protections, Bush and Blair may be liable to prosecution.

Certainly, they’d be advised to avoid too much foreign travel lest they end up like General Augusto Pinochet – placed under house arrest by a zealous administration determined to see them tested in a court of law. (Yes, it was us.)

I certainly hope it comes to that. So will the families of 3000 dead servicemen and half a million Iraqis. It is a terrible crime. They will not forget, and nor should we.