Britain will order a new Boeing C-17 military transport plane, Prime Minister David Cameron said Wednesday, after a programme of defence cuts freed up the required funds.

"This aircraft is becoming an absolutely brilliant workhorse for the RAF, in terms of bringing men and material into a warzone such as Afghanistan, but also in evacuating civilians in times of need," the prime minister told parliament.

"It is an important investment for the country and I'm glad to announce that we can make it today."

The Royal Air Force (RAF) currently has seven C-17s, into which military vehicles and cargo on pallets can be loaded through a rear door.

It is used to transport some of the 9,500 British troops stationed in Afghanistan.

Cameron's coalition government of Conservatives and Liberal Democrats announced deep cuts to the Ministry of Defence budget after it came to power in May 2010, blaming the previous Labour government for massive over-spending.