The BBC's Afghanistan correspondent Alastair Leithead is leaving the war-torn country after three years
Seven years after the Taleban was removed from power in Afghanistan some 7,800 British military personnel are still stationed in the country as part of the Nato-led International Security Assistance Force (Isaf).
Some of the fiercest fighting has been in Helmand province
The International Security Assistance Force in Afghanistan was Nato's first and largest ground operation outside Europe and even now the force comprises of more than 50,000 personnel drawn from 40 countries.
But despite this huge military presence, and millions of pounds invested in Afghanistan, violence and unrest is still ravaging the country.
One of the worst areas is the southern province of Helmand where three summers ago British forces began fighting Taleban and other anti-government forces, such as al-Qaeda, in earnest.
There from the start
When the campaign began, the-then UK Prime Minister Tony Blair and his government hoped it would be over without a shot being fired.
However, since then hundreds of UK troops have been killed or injured and the fighting is as fierce as ever.
121 British military personnel have died in Afghanistan
The BBC's Afghanistan correspondent, Alastair Leithead, was in Helmand when the British mission started and in Panorama: Three Bloody Summers we see him return for his third and final summer.
In the programme Leithead travels across the troubled region to assess whether the military strategy is working there, and whether it is worth the cost in British lives.
He visits a number of outposts from where British troops are pushing into combat, such as Garmsir an agricultural town right on the limit of British control which has seen some of the bloodiest battles.
By last summer Garmsir was a ghost town, its civilians having fled to escape the fighting.
But that has now changed. This year the locals reclaimed their town and instead of an urban battleground Leithead finds a busy market town, where it is now safe enough for the BBC's film crew to walk in on foot.
In fact security has improved sufficiently for the governor of Helmand to make his first visit there in three years. But, as the hard stares from the locals and the small army of Afghan guards surrounding the governor attest, the town is still far from safe.
Just a week before, three British troops had been seriously injured in Garmsir when a roadside bomb had struck their vehicle.
The 200 tonne turbine had to be driven through Taleban territory
Rather than Afghanistan becoming safer for UK troops, the situation has, if anything, been getting worse.
Analysis of official casualty figures by the Medical Research Council (MRC) shows that 2008 has been the bloodiest year yet for coalition troops, and that in fact British forces are now being killed in Afghanistan at a faster rate than during the invasion of Iraq.
Afghan President Hamid Karzai tells Panorama that "the presence of international troops in Afghanistan is not enough to bring security".
"Security in Afghanistan can only be brought by the Afghans - and if we don't have the Afghan element - no matter how many hundreds of thousands of troops you bring in here security will not happen," the president insists.
'Road to nowhere'
But as Leithead reports, building an Afghan national army to take over the country's security has proven a difficult challenge.
And even harder has been trying to change to allegiances and attitudes of Helmand's tribal chiefs and elders. Our reporter finds that many in Afghanistan say a key stumbling block to winning hearts and minds has been the notion that Western-style solutions could be applied to an ancient tribal society.
And some have questioned whether the £20m a year being spent on development projects in Helmand province is being spent on the right things.
Leithead travels to the regional capital Lashkar Gah, home to a six-lane highway, which despite its £300,000 price tag currently goes nowhere, and a £400,000 pleasure park, which stands deserted most days.
But as Three Bloody Summers reports there has been progress too; the British authorities are building a popular local project that will provide water for 20,000 families.
And as Leithead travels north to the Kajaki reservoir he sees firsthand an even bigger project which could change lives across southern Afghanistan by providing electricity to one and a half million people.
Change of tack
But, as we see, for the project to even get underway necessitated one of the most audacious military missions since World War II as a 200 tonne turbine was driven 80km (50 miles) through Taleban territory.
Helmand's proximity to Pakistan's border is making life harder
Brigadier Mark Carleton Smith, the UK's most senior commander in Afghanistan, tells the programme that the security problems in Helmand are exacerbated by the region's proximity to the border with Pakistan, across which fresh Taleban fighters are able to pass at will.
As a result, according to Brig Carleton Smith "there is no exclusively military solution to the nature of the insurgency in Afghanistan".
And this is a view that others share - frustrated by having failed to crush the Taleban through military might, some are now asking if it is time to start talking to elements of the enemy as well.
In his final weeks in Helmand, Leithead flies to Musa Qala, a town on the northern edge of British control, now the scene of a remarkable experiment where a former Taleban commander has been persuaded to switch sides and is now in charge.
It asks a question as to whether talking to the Taleban could be the way forward.
Three Bloody Summers, Monday 3 November at 8.30pm on BBC One.