More than 4500 Taliban insurgents have defected since 2005 and up to 4000 others have been killed in action against British and Canadian forces in southern Afghanistan, according to military intelligence sources.

Many are believed to have deserted the militant side as a result of a combination of persuasion by British and Afghan government agents and the realisation that they could never counter Nato airpower, the single biggest cause of their losses in battle.

The latest intelligence briefing available to alliance military commanders says that the Taliban can field up to 10,000 fighters at any given time in the south and east of the country, but that only 2000 to 3000 of these are highly motivated, full-time jihadis.

The rest are locals paid up to £25 a day - the equivalent of about a month's wages for rural Afghan farmers - to pick up a gun and attack Nato troops.

A British officer with wide experience in Helmand told The Herald yesterday: "We reckon that the Taliban has lost perhaps two-thirds of its field commanders in Helmand and Kandahar in the last year or so. That has weakened its tactical structure, although it is unlikely to stem the flow of paid or religiously motivated recruits.

"Where the Nato countries represent an alliance of the willing, the Taliban is essentially an alliance of vested interests. There are religious warriors, drug lords who fear an erosion of their trade, simple poppy-farmers who take up arms to protect their livelihood and men sent by warlords to keep the pot boiling and deny Kabul control.

"It's been a central plank of Nato alliance strategy to try to divide and rule. There are British and other agents who speak the local languages and are versed in the labyrinthine tribal politics of the region working covertly to split support away from the hard-liners.

"It's hardly a new phenomenon. We were doing the same thing as an imperial power in the 1800s, only then the objective of The Great Game was to thwart Russian territorial ambitions and deny the czars the means of threat- ening our control of India."

A CIA source added: "Our best estimate is that 10% of the hardliners Nato faces are foreign jihadis, mainly Chechens, Uzbeks and Arabs. They have stepped in to fill the gaps left by the combat attrition of local Taliban midlevel leaders."

The core Taliban operations in the south are run by Mullah Omar, the movement's spiritual head, from a headquarters in Quetta on the Pakistani side of the Afghan frontier.

A second front is operated by the Haqqani clan in Paktia and Khost provinces to the north and east and a third in the north and west is controlled by Gulbuddin Hekmatyar, a warlord who has worked for the anti-Soviet mujahideen, the CIA and Pakistan in his time.