David Cameron: We can't stay a moment longer than is needed

The Conservative leader hardened up the party's stance on the issue, stressing that the British public needed to be reassured why their soldiers were fighting the Taliban.

And as Oxfam today warned that Afghanistan was not allocating foreign aid effectively, Mr Cameron also said that voters wanted to know what was being done to tackle corruption.

The Tory leader made clear that he wanted a shift in approach on the conflict. "The whole point about our involvement in Afghanistan is that we don't want to be there a moment longer than we have to be," he told GMTV.

"We just want to make that country secure and safe and run by Afghans so that they can take decisions about the future of their country so it can be free of terrorism."

He added: "Once [the elections] are finished, it's very important that we have a tough compact with the Afghan government about what they are going to do to cut out the drug dealing, to cut down corruption, to deal with the ineffectiveness of parts of the Afghan Government itself."

Although the Conservatives have criticised the lack of equipment for troops, they have for years given their broad support to the mission in Afghanistan. But shadow foreign secretary William Hague and shadow defence secretary Liam Fox would be keen to review Britain's approach under a Tory government.

Many Tory MPs want the party to focus on faster training of Afghan troops and police and would like a rough timetable for withdrawal.

Until today Mr Cameron has stayed out of the debate about Afghanistan's future, preferring instead to focus on the immediate operation to secure the presidential elections.

Chancellor Alistair Darling, who is standing in for the Prime Minister, today defended the campaign.

He said: "We have got to have a democratically-elected government in Afghanistan that can protect its people, that can ensure that it can get the political change that is necessary, as well as working with other countries to get security, not just for that region, but for the rest of us."

And he said: "What happens in Afghanistan does affect people in this country.

"We have seen that in the past with al Qaeda, with terrorist attacks, and we have got to make sure that we see this through and we get the democratic process going in Afghanistan."