Andrew Grice: How the Government's Afghan wires have become crossed

Any talk of dates makes military commanders wince since they know it only strengthens the enemy's resolve to sit tight, play it long and then claim victory

When is a timescale not a deadline? When you're a politician talking about pulling troops out of Afghanistan. When they held talks in Canada last weekend, David Cameron and Barack Obama realised they had something in common: the need to reassure their domestic audience that the commitment to maintaining forces in Afghanistan is not open-ended.

Mr Cameron did not mean to create a flurry of excitement by telling Sky TV at the G8 summit: "Make no mistake, we cannot be there for another five years." To him, it was a statement of the obvious, and he had said it before the May election. A lesson was learnt: saying something as PM carries a lot more weight than as leader of the opposition.

G8 leaders appeared to endorse Mr Cameron's five-year target, but closer inspection of their communiqué shows that all they did was call on the Afghan President Hamid Karzai to make concrete progress to "expand the capacity of the Afghan National Security Forces to assume increasing responsibility for security within five years." Not the same as a pull-out.

It is no coincidence that the next British election will be held in 2015. Mr Cameron is not the first politician to get a headline about withdrawing troops from Afghanistan by a certain date and then insist there is no deadline. President Obama has promised to start bringing home US troops from July 2011, even though the military "surge" does not peak until this November.

Any talk of dates makes military commanders wince since they know it only strengthens the enemy's resolve to sit tight, play it long and then claim victory. It could set back the "political surge" Mr Cameron wants to see in Afghanistan. Indeed, the BBC yesterday quoted the Taliban spokesman Zabiullah Mujahedd as saying: "We do not want to talk to anyone – not to Karzai, nor to any foreigners – till the foreign forces withdraw from Afghanistan. We are certain we are winning. Why should we talk if we have the upper hand, and the foreign troops are considering withdrawal, and there are differences in the ranks of our enemies?"

On the day of his first keynote foreign policy speech, William Hague had to reconcile apparently different signals from different ministers on the exit timetable. Speaking in Washington on Wednesday night, the Defence Secretary, Liam Fox, appeared to share the service chiefs' doubts about a deadline, saying that British forces could be among the last to leave Afghanistan. "The primary reason to be involved in a conflict is to win it, not to find the earliest exit," he said. "We must hold our nerve, maintain our resolve and have the resilience to see the job through." Premature withdrawal would be a "shot in the arm" to violent Islamic extremists around the world, he argued, and a "betrayal" of the sacrifices made by British forces.

Insisting there was no contradiction between Mr Cameron's and Mr Fox's remarks, the Foreign Secretary said: "We are committed to the Afghans being able to conduct their military operations and security and that takes time. But I would be very surprised if that took longer than 2014." He stressed that there is no timetable for withdrawal.

It is the second time since the election that ministers have got in a tangle over Afghanistan. Confusion arose when Mr Hague, Mr Fox and the International Development Secretary, Andrew Mitchell, visited the country in May. Mr Fox said: "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." But Mr Mitchell said it was "absolutely crucial" to build Afghanistan into a "functioning state" by providing basic education and healthcare facilities.

Although the media magnifies the differences between ministers, some MPs are worried. Sir Menzies Campbell, the former Liberal Democrat leader, said yesterday: "Singing off the same page of the same hymn sheet would be a very good idea."

Mr Cameron has warned of a "difficult summer" and military commanders believe that casualties will mount during the "surge" as the enemy is bound to fight back when under attack – as happened in Iraq.

A ComRes poll for The Independent and ITV News in April found that 72 per cent of the British public believe the war in Afghanistan is unwinnable.

Yet whatever the political pressures, it might have made more military sense to talk about leaving Afghanistan after the "surge" rather than during it. As James Arbuthnot, chairman of the Commons Defence Select Committee, put it neatly: "If our priority is to leave, that will make it harder to succeed, whereas if our priority is to succeed, that will make it easier to leave."