British troop withdrawals from Afghanistan are unlikely to begin next year, David Cameron warned today on a visit to the country.
The Tory leader suggested Government plans to hand responsibility for some Helmand districts to Afghan forces in 2010 had raised "false hopes" about the drawdown of UK troops.
He also said British troops were spread "too thinly" in Helmand and needed to be concentrated better.
Gordon Brown this week announced that a further 500 UK troops would be deployed in the conflict with the Taliban, taking Britain's presence to more than 10,000 personnel.
But the Prime Minister also wants international talks in London in January to set a "clear timetable" for the handover of power in Afghanistan.
He expects certain districts in Helmand to be handed over to local Afghan commanders next year, in what has been seen as an indication that British troops could be brought home.
But Mr Cameron told the BBC today: "I don't want us to raise false hopes. I think it's pretty unlikely that you are going to see a reduction in British troop numbers next year.
"But it should be based on success. The key here is, as soon as you can hand over lead responsibility to the Afghans in a district you should do, once it's safe.
"And once you're doing that you can bring down troop numbers in the future, but do it based on success, don't keep talking about artificial timelines."
Mr Cameron said President Barack Obama's announcement of a 30,000-strong US troop surge presented a "big opportunity" for success.
"The door is open, as it were, and we need to go through that door and do everything we can as quickly as we can to make progress and show we can have a successful outcome," he said.
But he said that there was an issue for British troops who were having to cover much more of the population per soldier than the Americans.
"We are spread too thinly," he said.
"I want to see the British forces more concentrated in areas where we can make a difference.
"And I think that's a decision we need to make relatively rapidly so that we can have forces in the thickness, in the density, amongst the people so we can actually do proper counter-insurgency, make a real difference and be a part of what I hope will be success."
Mr Cameron said an immediate withdrawal would be a "bad option", but added: "My view is very simple - we can't be here for another eight years."
He described the new Obama strategy as the "last best chance for success and we've got to take it".
Mr Obama has set July 2011 as the target date for the start of US withdrawals from Afghanistan after the forthcoming surge.
The Tory leader has travelled to Helmand, where he has spoken to locals at a market and addressed British troops at their Lashkar Gah base.
He was also meeting military leaders and Afghan president Hamid Karzai in Kabul, as well as watching Afghan forces train.
Mr Cameron has used the trip to promise to double bonuses paid to troops returning from Afghanistan.
He told reporters the payment for a six-month tour of duty would increase to £4,800 if the Conservatives won the general election expected next spring.
He also said he would appoint a national security adviser and have service personnel working at the Ministry of Defence wear uniforms instead of civilian clothing.
Speaking to The Sun about soldiers' bonuses, Mr Cameron said: "The pay they get for what they do is relatively low. We want to do more to make sure our forces have a better deal.
"I'll make that a priority of my first Budget. It will happen in our first 50 days."