The men from the SAS and the new Special Reconnaissance Regiment (SRR) will form a combined joint taskforce with members of the Australian SAS, according to senior defence sources. A company of British paratroopers will provide backup.

The British special forces of about 120 men will be based in the southern province of Kandahar ahead of a 5,500-strong infantry battle group expected to be sent early next year. There are currently 1,100 British troops in Afghanistan.

The British and Australian special forces will fan out across the territory to be covered by the British battle group. They will identify the most serious threats in the region and gather intelligence on any Taliban activity.

The troops face a hostile environment, with Taliban fighters regrouping in southern Afghanistan backed up by members of Al-Qaeda, including specially trained suicide bombers.

Last week RAF Harriers based at Kandahar joined US aircraft in providing support to American and Afghan forces in clashes in which 132 Taliban fighters were reported killed.

During their operations the SAS troopers will be assisted by the improved intelligence provided by a squadron from the SRR, which was formed this year to help in the fight against international terrorism.

Special forces commanders were warned months ago that they should be ready for Afghanistan. Senior commanders prepared what one source last week described as demands for “new Gucci kit” — requests for the latest equipment to spy on and fight the enemy.

The equipment, bought as a result of lessons learnt from the first SAS deployment during the war in Afghanistan, includes a spy plane the size of a child’s glider.

The American-made drone is launched by hand, can reach heights of about 100ft and operates to a range of more than five miles.

The SRR intelligence operators also have lightweight signals equipment capable of picking up mobile phone and radio communications.

The British will also be taking so-called “fire-and-forget” electronic jammers that can be planted at various strategic points to provide blanket disruption of Taliban and Al-Qaeda communications.

The intelligence operators will have laptop computers linked to the larger US drones such as the Predator and Global Hawk and to American aerial reconnaissance satellites to download imagery of Taliban positions.

They are also expected to take a number of Supacat six-wheel, all-terrain vehicles, which have powerful turbocharged V8 diesel engines. The vehicles will be fitted with a grenade launcher that acts like a scatter gun, allowing the SAS to regain the initiative if they are ambushed by Taliban or Al-Qaeda fighters.

The composition of the battle group heading for Afghanistan has not yet been decided. Military commanders were hoping to send 19 Light Brigade, the new light infantry formation, to form the main British force. But Brigadier Chip Chapman, its commander, has said he does not believe it will be operational in time.

The wars in Afghanistan and Iraq have led to a change in tactics for the SAS, which has traditionally worked in small patrols of four men. Teams now vary in size and some of the operations during the Afghan war were the largest mounted since the 1970s.

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