As their new overall commander, General Stanley McChrystal is careful to praise the dedication and performance of the British Forces in Helmand, but he does not shy away from pointing out Britain’s strategic failures.

“British Forces have done great work in [Helmand] for a number of years,” the new commander of US and Nato forces in Afghanistan said in his interview with The Times. “But we have never had the density of forces that would allow us to go into more than fairly limited areas and change the dynamic by actually staying.”

It is the arrival of 20,000 American troops — about 12,000 of whom are due to go to the southern provinces — that he believes will halt the slide in Helmand, allowing US and British Forces working in tandem finally to hold the ground they take and, he believes, build lasting Afghan government structures.

“I can never predict in actual time and loss of life [how long the war will last]. But as we have focused our strategy now on doing comprehensive counter-insurgency operations . . . that allow us to make it stick. If we are successful here then what British Forces are doing will be enduring.”

The general, 54, paid a visit to British headquarters in the Helmand district of Nad-e-Ali this week. “I went and talked to the organisation [the Welsh Guards] and their resolve is what I expected, but incredibly impressive,” he said. “The way they have been doing those operations has been with the professionalism that has been my experience since 9/11 with a number of different British units. They are doing very well.

“These are areas that the Taleban has burrowed into for a long time so to change the dynamic really requires that you go and root them out.”

General McChrystal arrived in Afghanistan last month after several years commanding special forces in Iraq. He is determined to end the costly bombing errors that he believes have threatened the entire success of the Afghan campaign.

Last Thursday, when he sent 4,000 US Marines on Operation Khanjar, a thrust into Taleban strongholds in Helmand, he wrote a stark tactical directive. “The Taleban cannot defeat us militarily, but we can defeat ourselves,” it said. “We will not win based on the number of Taleban we kill, but instead on our ability to separate insurgents from the centre of gravity — the people. Following this intent requires a cultural shift within our forces.”

The Times has learnt that since the directive came into force the proportion of gunfights that resulted in calls for close air support has dropped from 35 per cent of all engagements to 17 per cent. Seven dead British soldiers in one week, and a significantly large number of wounded personnel, will be testing General McChrystal’s claim that he has to put his men at increased risk now to save lives later.

The soldier from 22 Engineer Regiment, Royal Engineers, who died in a helicopter crash in neighbouring Zabul province on Monday was named as Captain Ben Babington-Browne, 27, from Maidstone, Kent.

So far the US general’s fighting philosophy is unwavering. “One thing I would want the British public to know is that there are multiple ways to do this and one of them is to use overwhelming firepower,” he said. “We could use artillery and airpower and that would do tremendous damage to the infrastructure and cause a tremendous number of civilian casualties — and in so doing we would probably seal the fact that we would lose the fight over time, because we would convince the Afghan people that no matter what we said, we are not much concerned about their wellbeing.”

He added: “Even if all our good intentions say we are here to save them it goes back to the old cliché of ‘we destroyed the village to save it’. If you own the village you feel differently about that. If we operate in a way that creates damage or that actually, God forbid, kills innocents, it is pretty hard to see how the population could do anything but associate our arrival with something that hurts them.”

During the summer of 2007, British and other Western forces operating in Helmand called in an average of 22 tonnes of bombs per month — almost half the bombs that fell on Afghanistan at that time. Some of that dependency on air power would appear to have come from the under-resourcing of the British mission. “If you go back to 2006 you had Helmand [Task Force] come in. Although it was a fairly robust force in the equipment it was given, it was given tasks wider than its numbers allowed it to do.”

Times Recommends

• Both sides blame US for worsening relations
• Stieg Larsson: losing the plot over his cash
• Odd creature paralysed by incompatible parts