Gordon Brown's Government has denied that the UK has been involved in any negotiations with the Taliban despite the Prime Minister's declaration during his recent visit to Afghanistan that the time has come to talk to the Islamist movement.

However, senior British officers currently involved with the Afghan mission have confirmed to The Independent that direct contact with the Taliban has led to insurgents changing sides as well as bringing intelligence which has led to their leaders being killed or captured.

The British authorities hold that there are distinct differences between different "tiers" of the Taliban and that it is essential to try to separate the doctrinaire extremists from others who are fighting for money or because they resent the presence of foreign forces in their country.

However, the policy of engaging with the Taliban is hugely contentious. Critics, some of them members of Hamid Karzai's government, argue that this betrays the principle of establishing democracy in the country and also allows the Taliban to re-establish control under another guise. It is also claimed that large sums of money have changed hands on occasions in return for information.

To maintain the public stance that it is the Karzai government which is solely responsible for contact with the insurgents, all clandestine meetings take place in the presence of Afghan officials. Similarly, the defections of Taliban commanders are credited to purely Afghan efforts. However, according to UK and Afghan sources, British military as well as intelligence officials have travelled from the capital, Kabul, and Lashkar Gar in Helmand to meet members of the Taliban in southern Afghanistan.

One of the most successful military operations resulting from these contacts, it is claimed, was the killing seven months ago of Mullah Dadullah, the movement's commander in Afghanistan. Dadullah is said to have been tracked from information supplied by rivals in the Taliban movement before he was shot dead by a unit of the Special Boat Service in Helmand.

One officer with knowledge of the attack said there was initial suspicion that false information had been given after the British troops failed to find Dadullah's body following the firefight. Subsequently, however, the body was discovered along with a group of Taliban survivors who were trying to carry it away.

Other successful missions resulting from talks with the Taliban, according to defence sources, was an air strike which killed a Taliban commander near Musa Qala in February this year, and the rescue of two Italian hostages by members of the Special Boat Service in September.

But there have been claims that the insurgents may have used British and Nato forces to settle scores within their ranks and to eliminate rival commanders. Afghan military sources say, for instance, that the Taliban commander killed in February was in fact someone who was considering changing sides.

Some senior American officials have also claimed that the policy of engagement by the British has led to serious mistakes. The most symbolic of the differing views was the agreement reached in Musa Qala under which UK forces were withdrawn in return for tribal elders pledging to keep the Taliban out. The Taliban, however, took over the town and held it for seven months until they were cleared by British, US and Afghan forces a few days ago.

The British maintained that the Musa Qala negotiations were conducted not with the Taliban, but leaders of the community. Conceding that some of them may have been former insurgents the American interpretation is that the elders were sympathisers and some of them members of the Taliban.

Critics point out that after the Musa Qala agreement Islamic laws, some of them contradictory to the Afghan constitution were introduced. Assadullah Wafa, the governor of Helmand said: "There were things in the Musa Qala agreement that I was very surprised by. I have drawn up a protocol which makes sure that the government of Afghanistan actually rules that place. We cannot allow our enemies to have sanctuaries anywhere."

Insurgents who have dealt with the British and the Afghan government have sometimes paid the ultimate price. Some have been executed by their comrades and there were reports before the retaking of Musa Qala of a number of people, including children, being murdered as collaborators.