The government announced Thursday a 408-million-pound upgrade for its Chinook helicopters in Afghanistan, following criticism of a shortage of air power there.

The 38 aircraft will be fitted with more powerful Honeywell engines and more advanced digitised cockpits, to enable them to work more effectively in high altitudes and extreme temperatures in Afghanistan, officials said.

The upgrade to the twin-rota heavy lift choppers will notably allow them to fly longer without refuelling, and to spend longer on the frontline without needing to be serviced.

"The Chinook is the cornerstone of our helicopter support effort in Afghanistan," said junior defence minister Quentin Davies.

"These improvements will increase its capability and ensure it can play an even more valuable role in supporting our forces and NATO coalition allies in tackling insurgency in Afghanistan," he added.

Claims of a shortage of helicopters were at the centre of a political row over inadequate equipment for the armed forces amid a surge in the British death toll in Afghanistan earlier this year.

Prime Minister Gordon Brown has defended the government''s strategy in Afghanistan, after British forces have in recent months suffered their highest casualty rate since the US-led invasion of the country in 2001.