This is a timeline of key events in the UK's military involvement in Afghanistan.
* September 11: Nearly 3,000 people are killed when al Qaida terrorists hijack four passenger aircraft and crash them in New York, Washington DC, and Pennsylvania.
* October 7: Then-prime minister Tony Blair confirms that British forces are involved in US-led military action against al Qaida training camps and the Taliban regime in Afghanistan.
Royal Navy submarines fire Tomahawk missiles and RAF aircraft provide reconnaissance and air-to-air refuelling capabilities in support of US strike aircraft.
* November: The first UK troops are deployed to Afghanistan when Royal Marines from 40 Commando help to secure Bagram airfield.
* November 12: The Taliban retreat from the Afghan capital, Kabul.
* December 7: The Taliban lose their final stronghold, the southern city of Kandahar.
* December 22: The Afghan Interim Authority, headed by Hamid Karzai, takes office in Kabul.
* January 7: Mr Blair visits Bagram airfield to meet Mr Karzai and thank troops from the UK and partner nations preparing for the deployment of the Nato-led International Security Assistance Force (Isaf).
* April 9: Private Darren George, 23, from the Royal Anglian Regiment, becomes the first British serviceman to die in Afghanistan since the start of the mission.
An inquest later hears he was shot and killed patrolling the streets of Kabul by a colleague who suffered a dizzy spell as he handled his machine gun.
* October: Mr Karzai wins presidential elections with 55 per cent of the vote.
* January 26: Then-defence secretary John Reid announces that around 3,300 British troops will be deployed to Helmand Province in southern Afghanistan later that year.
* April 23: On a visit to Kabul Mr Reid says he would be "perfectly happy" if UK troops leave Helmand in three years "without firing a shot".
* July 10: New defence secretary Des Browne says the number of UK forces in southern Afghanistan will rise to 4,500 in the autumn.
* August 10: Lieutenant General David Richards, the British commander of Isaf, says UK troops in Helmand are engaged in some of the most intense and prolonged fighting seen by the Army for half a century.
* September 2: Fourteen UK servicemen are killed when their RAF Nimrod spy plane explodes in mid-air near Kandahar minutes after undergoing air-to-air refuelling.
* December 10: The Afghan Defence Ministry announces that the key strategic town of Musa Qala in Helmand has been recaptured from the Taliban after heavy fighting by British and Afghan forces.
Insurgents overran the town in February 2007 after the pullout of UK troops following a controversial peace agreement which gave responsibility for security to the Afghan elders.
* March 1: Prince Harry flies back to the UK after serving with the Army in Helmand when foreign websites break a media blackout on details of his deployment.
* June 8: Three soldiers are killed in a suicide attack, taking the number of British military personnel killed in Afghanistan since 2001 to 100.
* June 17: Lance Corporal Sarah Bryant, 26, of the Intelligence Corps becomes the first British servicewoman to die in Afghanistan.
* August-September: More than 2,000 British troops lead an operation to transport a huge new hydro-electric turbine 110 miles by road through Taliban territory to the Kajaki dam in Helmand.
* July 1: Lieutenant Colonel Rupert Thorneloe, commanding officer of the 1st Battalion Welsh Guards, becomes the most senior British Army officer to die on operations since the Falklands.
* July 9-10: Eight British soldiers die in 24 hours, including five members of 2 Rifles who are killed in two connected blasts near Sangin in Helmand.
* July 27: Prime Minister Gordon Brown hails the success of a fiercely fought five-week British-led offensive, known as Operation Panther's Claw, to drive the Taliban out of a former stronghold in Helmand.
* July 30: Official statistics reveal that July has been the bloodiest month for British forces in Afghanistan since the mission began, with 22 soldiers killed and scores more wounded in action.
* August 15: The death of Fusilier Shaun Bush, 24, of 2nd Battalion The Royal Regiment of Fusiliers, in hospital in Britain from injuries sustained in Afghanistan brings the UK death toll to 200.
* August 20: Afghan presidential and provincial council elections are held, but they are marred by violence, low turnout and fraud.
Mr Karzai is provisionally declared the winner, but he is forced to agree to a run-off vote with his main rival, former foreign minister Abdullah Abdullah, after investigators reject hundreds of thousands of ballots as fraudulent.
* October 14: Mr Brown announces he will send 500 extra British troops to Afghanistan, taking the total to 9,500, if a series of conditions are met.
* November 2: Mr Karzai is re-elected as president after Dr Abdullah announces his withdrawal from the second round of voting.
* November 3: Five British soldiers are killed by a rogue Afghan policeman in the Nad-e-Ali district of Helmand.