The British government is expected announce a further withdrawal of U.K. troops from Afghanistan, effectively halving its forces in the country by the end of next summer.

Up to 4,000 British troops serving in Helmand province in Afghanistan could head back home by next year, reducing the number of U.K. troops in Afghanistan to 5,000 from the present 9,500, Prime Minister David Cameron is expected to announce Wednesday, the BBC reported.

The decision came after the U.S. president and the U.K. prime minister agreed to accelerate their troop withdrawal in a video conference on Tuesday. The U.K. held a National Security Committee meeting on Tuesday to discuss the withdrawal timetables for the next year, which called for downsizing U.K. troop strength in Afghanistan to 5,000 by next autumn, the Telegraph reported.

However, the speeding up of the withdrawal process has raised concerns among British commanders, who believe that a more cautious approach is required in withdrawing troops.

Although the commanders agree with Cameron on the need to bring troops back home, they feel that halving the number of British troops in Afghanistan by next autumn will put extra pressure on the native Afghanistan forces, which are being trained by NATO-led commanders to manage their own security and combat operations independently.

However, there is increasing agreement among the commanders on ending the combat operations and bringing back additional troops in 2013, U.K. defense secretary Philip Hammond told the Guardian.

"I think that the message I am getting clearly from the military is that it might be possible to draw down further troops in 2013. Whereas six months ago, the message coming from them was that we really need to hold on to everything we have got for as long as we possibly can, I think they are seeing potentially more flexibility in the situation,” Hammond said.

Prime Minister David Cameron discussed the details of the withdrawal plans with the U.S. president in an hour-long video conference in which both sides agreed to “bring more troops back home” by next year, officials at 10 Downing Street said in a statement Tuesday.

"On Afghanistan, they discussed progress on the plan to hand security responsibility from ISAF to the Afghan National Security Forces, and they agreed that the NATO strategy to withdraw combat troops from Afghanistan by the end of 2014 was on track. This would present further opportunities for ISAF countries to bring troops home next year, and they agreed to stay in close touch as detailed plans develop,” the Downing Street statement added.

"They also agreed on joint work to strengthen the political process, particularly supporting Afghanistan and her neighbors to work together for stability, building on the trilateral discussions with Pakistan led by the U.K."

Details and decisions regarding the withdrawal will be finalized in the New Year, after taking into account the concerns of the commanders.  

The U.S., which has about 60,000 troops in Afghanistan, is also expected to announce its plan for withdrawing troops in January. The U.S. withdrew about 23,000 troops in 2012.