This is driven by poll ratings, not by conditions in Iraq

Tony Blair has always said that there would be no "artificial timetable" for pulling British troops from Iraq. Their departure would depend on conditions. His announcement yesterday of a minor reduction in troop levels this year reveals what those conditions are: the state of his poll ratings and the degree of movement he is allowed by George Bush.The prime minister is desperately trying to get a last surge from a British public that has long been disillusioned with the war, while not embarrassing an American president who is slumping at home even as he surges in Baghdad. Withdrawing less than a quarter of the British contingent in Iraq is Blair's attempt at balance. It will satisfy nobody, least of all the British military who would like to have wrapped up the entire Basra adventure this year or last. Now it will be up to Gordon Brown to show whether he has the courage or the survival instinct, in a few months' time, to make 2008 the year of the full pull-out. Defeating David Cameron may depend upon it.

Tony Blair pointed out yesterday afternoon that there is no Sunni insurgency in Basra, no al-Qaida, and very little Shia v Sunni violence. The last point applies because the Sunni community is too small to fight back, and up to two-thirds of them have been forced to flee. Basra's Christians are also escaping while they can. So, then, who is the enemy? The prime minister did not go into detail in yesterday's announcement, although everyone knows that it consists of a cocktail of different Shia Islamist militias, armed tribes and criminal gangs. Dealing with them cannot be the task of an army, either foreign or Iraqi. It is a job for police.

The task is made harder in Basra by the fact that the two main militias, the Badr organisation and the Mahdi army, are linked to different Islamist political parties that are vying for supremacy. The governor of Basra and the chairman of the provincial council have ties to one side, and the police chief to the other, while the police force beneath him is packed with men from both. They are engaged in a kind of civic civil war, a local struggle over who controls revenues, both legal and illegal - the most lucrative of which is the siphoning-off of Basra's oil.

None of this lethal crew likes the British, so it is no surprise that British casualties over the past four months have tripled as troops go valiantly about Operation Sinbad, an effort largely aimed at "cleaning up" some of the city's police stations. The Ministry of Defence keeps no monthly count of attacks on British troops, but the figures for the wounded who are taken to field hospitals have gone up from a rate of five a month between February and October 2006 to 17 a month since then. On the plus side, the MoD claims that in terms of reduced corruption 55% of police stations are now considered "acceptable", compared with only 20% when Sinbad began.

But the larger question remains. Why are British troops being asked to do this at all, especially as it is highly probable that the struggle within the Basra police will continue long after the British have gone? Before Sinbad began, extensive areas of Basra were a no-go zone for law enforcement. They will undoubtedly revert.

It is foolish enough for the Bush administration to think it can use American troops to end the civil war in Baghdad and Iraq's last few mixed cities. It is even more foolish for Downing Street to think it can end a civil war that is raging inside a police force. Britain's military commanders are pragmatic enough to know this, which is why they have long been hoping for orders to leave. They are not swept along by ideological naivety or inappropriate notions of a war on terror with its front lines along the Shatt al-Arab waterway. What they see in Basra is Chicago circa 1927, not Jihad Central 2007.

Britain's soft approach of leaving the Islamist militias largely alone, at least before Sinbad, has worked little better than the harder American one according to Anthony Cordesman, an independent analyst at the Centre for Strategic and International Studies in Washington. "The British were not defeated in a military sense, but lost in the political sense, if 'victory' means securing the south-east for the central government and some form of national unity," he says. "Soft ethnic cleansing has been going on in Basra for more than two years, and the south has been the scene of a less violent form of civil war for control of political and economic space that is as important as the more openly violent struggles in Anbar and Baghdad."

If Blair believed in a genuine "conditions-related" withdrawal, he would have brought Britain's troops out of Iraq two years ago. In January 2005 Basra's provincial elections put the present rulers in power. Voters there and in the three other Iraqi provinces under British command went to the polls with scarcely a mortar fired or a grenade launched. The occupation spin machines painted a picture of brave voters "defying the terrorists" as they cast the first free ballots of their lives for local and national government. Whatever truth there was in this appealing image in Baghdad, it did not apply in Basra.

At the city's polling stations, the long queues I watched were certainly impressive and poignant. There was a strong element of collective celebration - but one in which the militias and the parties to which they were linked also took part. Why bomb voters when you have candidates running and they are almost certain to win?

With no insurgents or al-Qaida in sight, British troops could have left south-eastern Iraq in 2005 as Robin Cook, Douglas Hurd and Menzies Campbell suggested at the time. Instead, their image as occupiers has become increasingly provocative even as the tasks they are assigned to do have grown more futile. Had they left Basra after the January 2005 elections, they could have claimed victory. When they go next year, leaving a local civil war behind, their departure will inevitably look like retreat.

Jonathan Steele