The Iraq war and its aftermath cost the UK almost £3.1bn up to the end of March this year, new figures from the Ministry of Defence (MoD) reveal.
The MoD says the conflict has rid the world of a "dangerous dictator"
The ministry's annual report shows troops' operations in Iraq cost £910m in the last financial year, compared to £847m in 2002/3 and £1.3bn in 2003/4.
Overall, the MoD spent £1.1bn in the year to March, including £67m in Afghanistan and £87m in the Balkans.
Opponents of the Iraq war say an astonishing sum has been spent on it.
Andrew Burgin, from the Stop The War Coalition, said: "It is a huge amount and every pound has been misspent and could have been better spent on schools and hospitals.
"It is a complete waste of money and resources - and a waste of human life on an illegal, unpopular and immoral war."
But a Ministry of Defence spokesman said: "We believe that the operations in Iraq were the right actions to rid the world of a very dangerous dictator."
The costs of the conflict in Iraq essentially come from government contingency reserves.
Ministers say remarkable political progress has been made in Iraq, with a new constitution approved in a referendum, and that security is also improving.