Leading article: Afghanistan: we must leave now

Nothing that has happened since Remembrance Sunday, November 2009, has changed our view that British forces should immediately begin their withdrawal from Afghanistan. At the time, The Independent on Sunday described the war as "ill-conceived, unwinnable and counterproductive". We became the first British national newspaper to say that our military mission should be ended: "It is time to start planning a phased withdrawal of British troops," we wrote, suggesting that we should "wind down combat operations" over the following 12 months.

Since then, David Cameron used the leverage afforded by a change of government to put a time limit on the British commitment: the end of 2014. Soon afterwards, Barack Obama completed his long – either indecisive or thoughtful, according to taste – review of US operations in Afghanistan and coincidentally came to the same conclusion. Whether that is better or worse than the previous open-ended commitment is a difficult judgement: it could be the worst of both worlds. If Nato forces are going to stay, their departure date should be defined by their mission. If they are going to go, they should get on with it.

Our conviction that a rapid pull-back from a combat role is the best option is not shaken by our report today that none of the Afghan security units is yet ready to take over responsibility. The handover to Afghan forces was supposed to start around now, according to the latest of an endlessly sliding series of timetables – the first timetable started slipping soon after the Taliban regime was toppled nearly 10 years ago.

At some point, Nato's political leaders have to take the courageous decision, which is to admit that they will have to leave with their task incomplete. The problem is that this task has been redefined and expanded from the limited original purpose of the intervention. Mission creep has happened many times before, yet it is always hard to admit what is happening at the time.

Yes, there will be unpleasant consequences of withdrawal, but this newspaper's argument has long been that some of the consequences of our presence are pretty unpalatable, and the net benefit to the Afghan people – let alone to British national security – of our presence there does not justify the cost in British lives.

British forces have done good things in Afghanistan, and The Independent on Sunday's argument is that they should continue to do them. It is no disrespect to their service if it is decided that their role should shift away from combat. They should support civil construction, and they should continue to help train the Afghan army and police force. But they should not be fighting the Taliban, except with special forces or from the air, if that is needed to prevent al-Qa'ida from returning to the country. That, it should be remembered, was the reason for Nato's intervention in the first place.

As Liam Fox, the Defence Secretary, said soon after he took office in May last year, "We are not in Afghanistan for the sake of the education policy in a broken 13th-century country. We are there so the people of Britain and our global interests are not threatened."

The failure of Nato and the Karzai government to bring Afghan forces up to the level at which we judge that they would be capable of providing security is not, then, an argument for continuing the failed policy of the past nine years. If they are not "ready" by that definition now, what makes us think that they will be "ready" by the end of 2014?

It has become ever clearer that we should pursue a different policy, of seeking a political settlement with the Taliban and other anti-Western forces, and of accepting that Afghans will have to take responsibility for their own security, however unready they may appear to be.

Nor is there anything to be gained by staying in the battlefield simply to provide political support to the Obama administration. The last British troops pulled out of Iraq last month, while there are still 47,000 members of the American armed forces there, and some of them are likely to stay beyond President Obama's (latest) deadline of the end of this year.

Nothing of value will be achieved in Afghanistan by trying to win the military "victory" over the Taliban during the next three and a half years that has eluded Nato over the past nine and a half. Britain should set a new 12-month timetable and start to "wind down combat operations" now.