As Geoff Hoon confirmed for the first time that British troops were on the ground in Afghanistan, experts said they were likely to be members of the special forces.

The Defence Minister would not verify the presence of special forces but the highly trained warfare experts have probably played a crucial part in the war against the Taliban and the al Qa'ida network.

America made public the presence of its forces within Afghanistan several weeks ago, but British ministers have skirted around the subject. "I can certainly confirm that there are members of Britain's armed forces on the ground in northern Afghanistan, liaising with the Northern Alliance, providing advice and assistance," Mr Hoon said yesterday.

"The situation on the ground is enormously encouraging, there is real momentum. I accept that there has been criticism ... that the bombing did not appear to be achieving results.

"But it has been vindicated because we have seen the collapse of the Taliban regime around Mazar-i-Sharif, and that is why the bombing in recent days has been concentrated on those front lines."

The British troops in Afghanistan, unlikely to be more than 100, are probably gathered from the Special Air Services and Special Boat Service aided by a few pathfinders from The Parachute Regiment.

British signallers and engineers are known to be stationed in central Asia, on stand-by to repair the airport at the strategically vital city of Mazar – taken by the Northern Alliance two days ago – for use as a military base by Allied forces. But whether they have been deployed is not known.

Special forces onreconnaissance missions will work in teams of four. They will be backed up by larger units, which will co-ordinate military planning with anti-Taliban groups and also ensure they have adequate logistical supplies. The British, in particular, have been pressing for "human intelligence" rather than the "hi-tech" information from Predator spy planes and satellites favoured by the Americans.

Surveillance, identifying targets for air strikes, forging links with local communities and assisting the Northern Alliance with tactics are likely to have been among their main roles.

Mike Yardley, a defence expert, said yesterday: "The SAS would be mainly deployed in three roles and one can assume they have been there since the very early stages of these proceedings.

"The first is gathering intelligence on the Taliban and presumably also looking for Osama bin Laden.

"The second is acting as forward observation officers to target in laser guided weapons and pass on communications.

"The third is to act as some sort of snatch, destroy or killer group to attack bin Laden or his lieutenants in their lairs and we would expect them to be backed up by other forces for that role such as the US Rangers.

"It's also likely the SAS will be trying to win over the hearts and minds of the local communities ... Once you've got them onside you will receive benefits from them such as intelligence."