Leading article: Our narrowing options in Afghanistan

It is hard today for any political leader to defend the West's policy in Afghanistan with much conviction. A war that began with the almost effortless expulsion of the Taliban from Kabul 11 years ago has run into the sand, like so many Afghan wars before it. A campaign initially seen by many as just, because of the Taliban's protection of Osama bin Laden, has lost its last shreds of purpose.

David Cameron's visit to Afghanistan this week, his first for 12 months, served to cast the problem into sharp relief. He had to defend a war that still claims soldiers' lives, long after it has lost its point. Military officials may describe this year's 20 per cent troop reduction, leading to a total pull-out in 2014, as a "glide path down", but the plainer term would be a scuttle.

Mr Cameron admitted that the decision to slash the British presence was a difficult one, but insisted that he could "look all the Armed Forces in the eye" because it was the right thing to do. Right or wrong, the awkward truth is that he had very little choice in the matter. The pretence that Britain had any kind of autonomous Afghanistan policy was fatally undercut when President Obama decided on the total withdrawal of US forces by the end of 2014. Then in May, the newly elected President Hollande announced that French forces would withdraw by the end of 2012. Britain has no option but to depart when the US does. The plan to leave behind a military academy is little more than a fig leaf to cover the shame of a mission blighted by unjustified optimism.