In Vasily Grossman's remarkable novel Life and Fate, there is a powerful scene in which two Bolsheviks encounter one another as prisoners in one of Stalin's labour camps in 1942. The younger Bolshevik, Abarchuk, who is convinced he is there in error, remains a believer in the cause; but his older mentor, Magar, has gained wisdom through experience. When the two comrades snatch what turns out to be their final conversation, Magar looks around the camp and distils their years of revolutionary experience in words of terrible simplicity and force. "We made a mistake," he tells Abarchuk. "And this is what our mistake has led to."It has become increasingly hard for a truthful person not to apply those same words to the situation facing the US and Britain in Iraq. It is not Stalin's Russia and Bush's Iraq that are the same, of course. It is the dreadful clarity of Magar's conclusion about the way events can evolve. In Iraq we too made a mistake. Adapting a comment by the 19th-century diplomat Talleyrand, I see Britain's role in the invasion not as a crime, but as an error - and the scenes of desecration and murder this week across Iraq are what our mistake has led to.Even if you supported the invasion - and I have always accepted that there were principled and respectable grounds for doing so - this simply was not what you expected, much less wanted, to see. No country can survive indefinitely with the level of violence, insecurity and - much less widely reported but far more widely experienced - continuing material discomfort that has now become the everyday reality in many parts of Iraq.The blowing up of the al-Askari shrine in Samarra on Wednesday was an act of pitiless destruction and malign calculation - as wickedly provocative to Iraqi Shias as the assault on the twin towers on 9/11 was to Americans. With at least 130 Sunnis killed since Wednesday, Shia leaders vacillating over calls for restraint, inter-party talks abandoned and three central provinces under daytime curfew, the provocation has already come dangerously close to achieving its goal.But we need to be careful not to rush fences here. There has been much talk this week about Iraq drifting into civil war. Such talk makes good headlines that reflect the seriousness of the situation. They do not, one senses, reflect the more complex reality that few of us can truly know, because it is so desperately hard and dangerous to report on what is happening outside the Baghdad Green Zone. A wider point of caution must also be considered. Drifts towards civil war can be long or short. There is no law of history that says they always end in conflict. Drifts are like declines and rises - always relative, rarely absolute - as Northern Ireland reminds us.The situation in Iraq, in other words, is very serious. But the only question worth asking about it is not how we got there but where we go from here. The clear answer - which is also, as it happens, the government's unacknowledged answer - is that we should get out in as good order as possible, as soon as possible, leaving Iraq with its best chance in all the circumstances. That doesn't necessarily mean quitting immediately. But it does mean planning to leave and then, over time, leaving. And there are more options to this than the week's events might imply.Violence is spreading, but it remains, relatively speaking, localised. The institutions of civil society undoubtedly differ in different parts of Iraq but, for all their weakness, they remain in place and continue to function. There is an elected Iraqi assembly and president. Dialogue is still taking place about forming a unitary government. Religious leaders are mainly a force for restraint. Most Iraqi security forces continue to be trained. Even the invasion forces, for all their caged impotence, can claim to have a general restraining influence - judged by the widespread assumption that violence would rapidly intensify if they were to take the next plane out. The US, in particular, continues to exert some restraining political and financial influence, even if its military influence is minimal.Whether this adds up to a critical mass of stabilising elements adequate to hold the shaking line against the forces of violence over the necessary period is a tough call. This week has undoubtedly made the task more difficult, and the invasion's apologists should not pretend otherwise. Tony Blair, at his press conference this week, talked as though everything is unchanged. But it isn't.Even the Iraqi president's man talked yesterday about the volatility, sensitivity and seriousness of the situation, while Britain's former post-invasion Baghdad representative Sir Jeremy Greenstock plundered his thesaurus for words that diplomats rarely deploy, such as damaging, delicate, fragile and unpleasant.So where do we go from here? In his book on America and Iraq, The Assassins' Gate, the New Yorker journalist George Packer observes at one point that too much American (and other) discussion about Iraq policy takes place in rigid moulds set by the second world war (the western "we will never surrender" paradigm) or by Vietnam (the "we will never win" alternative). Iraq, he insists, ought always to have been judged in its own terms, rather than being an arena for a defiant or fatalistic re-enactment of either of these earlier conflicts.That is a wise view that opponents and supporters of the war should both heed. If Packer is right then there may remain a working chance of a tolerably orderly outcome in Iraq in line with the experience since 2003, in which the violence recedes from this week's levels, the political talks reach agreement on a power-sharing government, and the invasion countries are able to draw down troop deployments before the US midterm elections, leaving Iraq to an uncertain but not inevitably disastrous future. It certainly wouldn't be the catharsis of Berlin 1945 revisited, but it wouldn't be the trauma of Saigon 1975 revisited either.This would be the best, or at any rate the least worst, outcome now. It is also, pretty obviously, the unacknowledged London and even Washington agenda. Ambitions have been scaled back. We don't want to be there any longer than we have to be. The Iraq war is over and Iran is the winner. Iraq's neighbours have an interest in making it happen. But it's time that the west's political leaders levelled with their voters about where things stand. We didn't exactly win. We didn't exactly lose either. We just made a mistake. And this is what our mistake has led to.