But this has proved not to be easy and London is now sending mixed signals.
Sir David Richards, the chief of general staff, says the mission in Afghanistan could last for as long as 30 to 40 years.
A statement that seems in tune with Liam Fox, the British defence secretary, who recently said that British troops will be among the last to depart from Afghanistan.
But aware of public opinion, David Cameron, the British prime minister, has made clear he hopes British troops can be pulled out of Afghanistan by 2015 - with the caveat that Afghan forces must be in a position to stabilise the country.
Just what is the actual cost of the UK military presence in Afghanistan? And for how long will the UK keep paying the price for its role in Afghanistan?
Joining the programme are Richard Kemp, a former commander of British forces in Afghanistan, Dan Plesch, the director of the Centre for International Studies and Diplomacy at the School of Oriental and African Studies, and Haroun Mir, the director of the Centre for Research and Policy Studies in Kabul.
This episode of Inside Story aired from Thursday, July 1, at 1730GMT, with repeats at 2230GMT, and the next day at 0430GMT and 1030GMT.
Source: Al Jazeera