A switch in Taliban tactics to use increasingly sophisticated home-made bombs has made this year the bloodiest for British forces since the Falklands War in 1982.
About three-quarters of the 100 UK deaths in Afghanistan in 2009 are thought to have been caused by insurgent-improvised explosive devices (IEDs).
This represents a conscious shift by the militants away from taking on Nato troops in pitched gun battles, which were invariably won by the better equipped and trained foreign forces.
When they come under fire from insurgents, UK soldiers can limit casualty numbers by calling in air support, but IEDs strike suddenly and without warning.
British troops have been hit particularly hard because nearly all of them are based in Helmand, a Taliban stronghold and major centre of opium production which is the most dangerous province in the country.
One expert said the growing complexity of the IEDs used in Afghanistan suggested that the Taliban were getting help from either state sponsors or - more likely - experienced Islamist insurgents who have fought in places like Iraq or Chechnya.
Dr Tim Bird, a lecturer in the defence studies department of King's College London, said: ''The Taliban changed their tactics about 18 months ago.
''Initially when we moved into Helmand in 2006, the Taliban were keen and eager to have pitched battles.
There has been intense debate this year about whether the equipment and vehicles provided to British troops in Afghanistan are adequate to protect them from insurgent bombs.
Some critics have blamed a shortage of helicopters for the high number of UK deaths, pointing out that personnel often have to travel around Helmand on land.
But Dr Bird said it was vital for troops to move among the local population in a counter-insurgency operation, adding that no vehicle was invulnerable to IEDs.
''I was talking to a few military guys about the general political debate about whether we need better vehicles,'' he said.
''I was expecting the military guys would all buy into that.
Similarly, having more helicopters would lead to the militants concentrating on targeting them, he said.
Dr Bird said the IEDs laid by the Taliban were ''clearly'' getting more complex, but played down the possibility of Iran being as heavily involved in supporting insurgents in Afghanistan as it was in Basra, southern Iraq.
''The people instructing the IED-makers probably will have experience in Iraq or Chechnya. That would explain the growing sophistication of the devices,'' he said.
UK forces were first officially deployed to Afghanistan in November 2001, when Royal Marines helped secure Bagram airfield as part of the US-led invasion following the 9/11 terrorist attacks.
Several thousand more troops followed but the human cost remained relatively low until Britain sent a taskforce to Helmand in spring 2006.
By the time the British military death toll in Iraq reached 100 in January 2006, there had only been five fatalities in Afghanistan.
Three months later the then-defence secretary, John Reid, said he would be ''perfectly happy'' if UK troops left Helmand three years later ''without firing a shot''.
This proved to be a massive misjudgment as the military became engaged in some of the fiercest fighting UK forces had experienced since the Second World War.
There were 39 British deaths in the Afghan conflict in 2006, 42 in 2007 and 51 in 2008.
The death toll soared this year as UK troops launched major missions over the summer to provide security in Helmand ahead of August's presidential and provincial elections.
Dr Bird said British commanders had set out a clear outline for the future direction of operations in Afghanistan.