Half of Britain's Afghan and Iraq helicopters unfit for purpose

A survey of its helicopter fleet also found a third of the Chinook transport aircraft were grounded whilst only around half of the ageing Sea King helicopters and the newer Merlin MK3 support choppers were operational.

The survey, carried out in August, shows the percentage in the 'forward fleet' considered fit for purpose at the time.

It showed that the Gazelle AH1, used for used for battlefield observation and reconnaissance, was the best performing model.

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It found 81 per cent of the Gazelles met the required criteria of being "available, reliable, airworthy and capable of carrying out their planned missions on a given date".

The number of available Apaches, which are attack aircraft, has declined from 60 per cent last year, the survey found.

Liberal Democrat defence spokesman Nick Harvey - who obtained the figures through a parliamentary question - said:

"They surely call into question the sustainability of our helicopter operations in Iraq and Afghanistan.

"It is particularly disturbing that since last year there has been a general fall in the number of helicopters fit for purpose.

"The pressure on helicopters in Afghanistan is particularly acute. If we are to be there for the long-haul then the Government must get to grips with the overstretch of our armed forces."

Mr Harvey called on ministers to hold an urgent strategic defence review.

Meanwhile A Ministry of Defence spokesman said that all helicopters on operations in Iraq and Afghanistan are considered "fit for purpose".

The percentages of helicopters 'not fit for purpose' applied to those in the UK or elsewhere unable to fly for reasons such as undergoing routine maintenance.

He said: "Our operational capability is measured in terms of flying hours not the number of airframes available, and we have sufficient helicopters and helicopter hours to meet essential operational commitments."

No figures for the numbers of helicopters the percentages are based on were available.

Three former defence chiefs warned last week that inadequate defence spending is seriously undermining UK efforts in Iraq and Afghanistan.

Lord Guthrie, Lord Craig and Admiral Lord Boyce want the annual defence budget raised from £34 billion to nearly £50 billion.

In a BBC interview yesterday, Chief of the Defence Staff Air Chief Marshal Sir Jock Stirrup said there were "robust" debates with Government over defence spending.

He acknowledged that overstretch was a problem, but insisted:

"Our equipment in theatre has improved out of all recognition over the last couple of years particularly in terms of force protection, protective patrol vehicles."

In 2002 many Apache helicopters were grounded due to a lack of trained pilots and were only deployed to Iraq years later.

Last year, it was revealed that the RAF was routinely dismantling helicopters to find spare parts to keep others flying, a practice known as "cannibalisation".

The Government revealed that spare parts were so scarce that one aircraft had to be dismantled to replace "a single nut" on another helicopter. Support aircraft including Chinooks, Merlins and Sea Kings were also regularly being dismantled.

Ministers revealed that in 2005, RAF helicopters had to be cannibalised on 1,599 occasions – more than 30 times a week.