Last week's television footage of a British soldier in flames, escaping from his armoured vehicle in Basra, was a possible turning point in this country's disastrous involvement in Iraq. One image captured the essential truths that Mr Blair would rather avoid: that the condition of Iraq is getting worse and that British troops are no longer regarded as protection against still worse horrors.
For a long time after the invasion, The Independent on Sunday resisted the demand for "troops out". Britain was wrong to take part in the invasion, but once Saddam Hussein was overthrown a simple maxim applied: "Who broke it, fixes it." The United Nations reluctantly entrusted the US and its allies with the legal and moral responsibility for the welfare of the Iraqi people. And the Iraqi people themselves, deeply torn between regarding the coalition forces as liberators and occupiers, feared the bloody consequences of foreign troops leaving too early.
That was then. This is now. It has been getting harder, and has now become impossible, simply to sit tight and hope that things will improve to the point where the Coalition can declare Iraq "fixed" and bring its troops home. It is now as obvious as it could be that the presence of foreign troops is the principal cause of the continuing and growing violence in Iraq.
It remains the case, however, that in parts of the country, including Baghdad, the incipient civil war between Sunni and Shia might be bloodier if the Americans were to pull out tomorrow. But that is not true of the British sector in the south. What the flames from the petrol bombs illuminated in Basra last week is the fact that many of the Shia who are represented in the government in Baghdad regard the British forces as being against them. The Shia should be able to run the south themselves; the British presence is still there largely to provide political cover for the Americans in the north.
This is emphatically not to argue that we should disown our responsibility to the Iraqi people. But there comes a point when we have to ask whether that responsibility is best discharged by staying or going. We have to avoid repeating the mistake of unpopular occupations throughout history, insisting that our obligation is to "see it through".
The occupiers of Iraq have already repeated too many of the errors of the past, from blaming "forces from outside" to setting too much store by "milestones" such as next month's referendum on the constitution. All occupying armies outstay their welcome, but the US-led Coalition in Iraq was never particularly welcome in the first place.
The mindset of this occupation needs to change, therefore, from "as long as it takes" to a step-by-step strategy for withdrawal. The prospect of British troops leaving would be useful primarily as a way of putting pressure on the US administration to make that mental shift. Immediate US withdrawal may not be either desirable or remotely politically possible. But the Americans will bow to reality in the end. The only question is how soon they will face up to the fact that Iraq has gone wrong and is getting worse.
Meanwhile, the Prime Minister, at the subordinate end of the transatlantic alliance, must give up his policy of trying not to mention the war. The absence of an exit strategy leaves a dangerous sense of drift. His only hope of retrieving any honour from the flames of Basra is to set out the practical steps that need to be taken to make the withdrawal of British forces possible sooner rather than later.