British Prime Minister David Cameron, on an unannounced visit to Afghanistan, said on Tuesday he was confident British troops could start leaving early next year, when transition to Afghan forces begins. Britain has the second-biggest foreign troop contingent in Afghanistan after the United States, and Cameron, who was on his sixth visit to Afghanistan, has said he wants British troops out of combat roles by 2015. While he has said before he wants that process to begin next year, British commanders have since tried to play down the prospect of any major withdrawals in early 2011, saying it would depend on the readiness of Afghan forces to take over and other conditions on the ground. What Ive seen on this visit gives me confidence that our plans for transition are achievable beginning early next year, Cameron told a news conference in Kabul alongside Afghan President Hamid Karzai. As Cameron and Karzai spoke, US Defense Secretary Robert Gates arrived at the sprawling Bagram Air Base just north of the capital, Kabul.