UK troops have been providing security ahead of the Afghan elections
The growing toll of Britain's actions in Afghanistan has left some critics questioning exactly why troops are there.
Explanations from politicians and military leaders range from preventing terrorism and improving Afghan human rights, to promoting economic development and state-building.
The BBC's Caroline Hawley looks at some of the major questions surrounding Britain's daunting and wide-ranging mission.
Why are UK troops there?
British troops went to Afghanistan in November 2001 as part of an American-led invasion in the wake of the 9/11 attacks. The goal was to topple the Taliban who had given safe haven to al-Qaeda.
That goal was quickly achieved and in the following years the aims of the British mission broadened.
But in early August this year, the House of Commons Foreign Affairs Select Committee said British troops were trying to do too much.
"The UK has experienced mission creep from its initial goal of supporting the US in countering international terrorism, far into the realms of counter-insurgency, counter-narcotics, protection of human rights and state-building," according to committee chairman Mike Gapes.
The government - on the defensive over the rising death toll in Afghanistan - insists that Britain is fighting to protect its national security.
When the 200th British soldier died, Gordon Brown said: "The work of our troops - providing security, through operations like Panther's Claw, building up the Afghan army and police, and allowing politics and economic development to take root - is vital to preventing al-Qaeda once again using Afghanistan as a base for terrorist attacks against Britain and other countries."
The Ministry of Defence says that multinational forces in Afghanistan have a common goal: "To develop a self-sustaining, stable and democratic Afghanistan."
What are British forces doing?
There are now 9,000 British troops in Afghanistan, with the vast bulk - 6,200 - in the southern province of Helmand.
They moved into Helmand - a Taliban stronghold - in the spring of 2006 when then Defence Secretary John Reid said their mission was to help Afghans reconstruct their economy and democracy.
But they swiftly ran into strong armed opposition and there has been fighting in Helmand ever since.
The aim of the operation in the province at the moment is to "clear, hold and build" - to capture land from the Taliban, control it and then begin reconstruction there.
At present, coalition troops are also helping the Afghan authorities organise this week's elections.
British and Americans helicopters are, for example, flying ballot boxes to remote villages.
How long will the UK have to be there?
That's the six million dollar question and, obviously, a matter of intense public interest.
The latest three soldiers named by the MoD died in an explosion
There are growing questions about whether the war that British troops are fighting is actually winnable and Army chiefs say that Nato troops will be needed until Afghan security forces can take over.
"That'll take a few years," says the outgoing head of the army, Sir Richard Dannatt. "I don't want to put a figure on that, but certainly two to four years, three to five years, of this kind of level of commitment by the military."
The incoming head of the army, Sir David Richards, has said he believes Britain will be committed to Afghanistan in some form for 30 to 40 years.
What challenges do British forces face?
When the British first moved into Helmand, troops were being attacked head-on at the bases they established.
Since then, however, the nature of the fighting has changed, and the main challenge now is the insurgents' use of "improvised explosive devices" or home-made bombs.
These have proved increasingly lethal and the vast majority of soldiers being killed in Afghanistan are dying in such explosions.
The military knows it has to find new ways of countering this growing threat and is already working on better armouring of vehicles.
The use of aerial drones to spot insurgents laying bombs is also being explored, but there has been growing concern in Afghanistan about the number of civilians killed in US drone attacks so they would have to be used with care.
More broadly, one of the biggest challenges for the British operation is to isolate the Taliban from the local population.
Have there been any successes?
The recent offensive in part of Helmand, Operation Panther's Claw, has been declared a tactical success.
Crowds now regularly turn out when bodies are repatriated
Officials say it has freed about 80,000 people from Taliban control and will enable those of voting age to cast ballots.
The problem is that the Taliban have simply moved on to attack British troops elsewhere in the province.
Both the government and the military say that this week's elections are crucial. The hope is that a stable government - backed by enough of the Afghan population - will help improve the overall security situation around the country.
But there's a widespread belief in the military that more boots are needed on the ground - both to fight and to train the Afghan security forces.
It is expected that the US will soon ask Nato countries to provide more troops, and the aim - in the medium term at least - is to substantially increase both the numbers and capabilities of the Afghan security forces who are a key element of any eventual exit strategy.
What other countries are fighting and how heavy are their losses?
At the moment, there are some 64,500 troops in Afghanistan representing 42 different countries - from Albania to Australia, Singapore to Spain.
They are working under a Nato umbrella and under the overall command of an American general, Stanley McChrystal, in an operation named Enduring Freedom.
The United States has the most troops - almost 30,000 - followed by Britain.
Many other countries send only a handful of soldiers - Georgia, with the smallest contribution, has just one.
The US has taken the most casualties, losing 785 soldiers, while Britain has the second highest toll, currently 204.
Canada, meanwhile, has lost 127 soldiers and Spain 25.