One man, one question: where is Bin Laden?

The confusion over yesterday's alleged claim by the Taliban ambassador to Pakistan that Osama bin Laden had left Afghanistan proves one thing: no one has any idea where the al-Qa'ida leader really is.

The US-led coalition, which has spared no resources in its search for Mr bin Laden, will simply file the latest reports under "information received" and carry on looking. Finding him would be the final act of the war, and they are getting closer.

In the skies above Afghanistan, spy satellites, fighter planes and unpiloted Predator drones are scanning the landscape. On the ground, US and British special forces, and anti-Taliban mujahedin, are seeking him out in helicopters, dune buggies and even on horseback.

In the past week, the area controlled by the Taliban – and therefore the territory in which Mr bin Laden can be confident of protection – has shrunk from nine-10ths to one-third of the country. "There is no reason to believe he's in Pakistan,'' the US Defense Secretary, Donald Rumsfeld, said. ''There is every reason to believe he's in Afghanistan.'' But where exactly, and how is the coalition going to find him and his al-Qa'ida lieutenants?

''They are looking for information," said Mr Rumsfeld. "They are killing Taliban that won't surrender and al-Qa'ida that are trying to move from one place to another."

The first significant scalp was confirmed yesterday, when the Taliban acknowledged that one of Mr bin Laden's deputies, Mohammed Atef, had been killed by an American air strike near Kabul last week.

If American intelligence is to be trusted, then the death of Mr Atef is a prize – he is the man who planned the bombings of two US embassies in Africa in 1998, and also a suspect in the 11 September attacks on New York and Washington. Is it just a matter of time before Mr bin Laden is netted, as the Taliban-controlled territory dwindles like the water leaking out of a pond? Or can a man well over 6ft tall, with one of the most famous faces in the world, simply disappear?

Several things make the task of physically tracking down Mr bin Laden immensely uncertain. Chief among them is the famously difficult nature of the Afghan terrain. Much of southern Afghanistan is desert, but the Taliban city of Kandahar is flanked to the north by mountains riddled with deep valleys and networks of caves.

During the Soviet Union's disastrous war in Afghanistan, there were legends about deep underground shelters into which the mujahedin retreated beyond the reach of Russian bombardment. Mr bin Laden's Saudi-based construction enterprise is said to have reinforced and refitted these during his residence in Afghanistan as a guest of the Taliban.

Mr Rumsfeld's briefings have made much of the activities of special forces, predominantly American, but also from other coalition partners, including Britain. He has displayed swashbuckling photographs of US special forces riding alongside the Northern Alliance on horseback in the north of the country. "In the south," he said, "they have gone into places and met resistance and dealt with it." But the other Pentagon briefer, Rear Admiral John Stufflebeem, said that American soldiers are not "roaming the country and looking to engage in fights".

The reason for this becomes evident when you look at the numbers of special forces in question – no more than 300 altogether, and only 100 in the south. The ground forces, it seems, are not teams of assassins, but liaison officers operating, in some cases, in ones and twos.

This is not to say that they will not get their man. They have put up roadblocks, blown up bridges and sought to funnel retreating Taliban and al-Qa'ida fighters into areas where they can be taken prisoner and questioned about their mentor's whereabouts.

If Mr bin Laden is captured or killed in Afghanistan, however, it is likely to be due to a perpetual element in Afghan history – tribal politics and betrayal. As the country slips away from the Taliban, fewer local leaders will be beholden to them, and more and more will see the advantages of delivering up their "famous guest", especially with a $25m reward on his head. But with few Afghan experts and fewer speakers of the local tribal languages, the allies must penetrate a dense screen of local politics and self-interest. Increasingly, too, members of the Taliban and al-Qa'ida will be captured – some, according to Mr Rumsfeld, are already in the hands of the Northern Alliance. "We do have some names," he said, "and they were not privates, some of them."

It is comforting to fantasise about a final showdown with Osama bin Laden – architect of terror, murderer of the innocent and sworn enemy of America. A chase across the desert perhaps, with US commanders in dune buggies in hot pursuit of al-Qa'ida horsemen, or a shoot-out in the bowels of a cave complex, between suicidal Arabs and potholing special forces.

But the more likely outcome is a body, or the remains of it, handed over for a ransom after a stab or a bullet in the back from one who appeared to Mr bin Laden to be a friend.