A research paper published by the House of Commons in September on the cost of Britain's international military operations reveals that expenditure in Afghanistan totalled £3.774 billion in 2010-11, very slightly lower than the year before. Total costs for the current financial year are likely to be £4.0 billion.
The report also provides details of the increase in troop numbers since June 2002 when there were only 400 UK troops in Afghanistan. Those seem like faraway days. Since April this year there have been around 9,500 military personnel deployed in Afghanistan, the highest figure ever in the present campaign.