The full assessment will be rolled out in the New Year

The MoD said questionnaires had been sent to troops to see if they had signs of mild traumatic brain injury (mTBI).

The survey was triggered by fears in the US Army that up to 20% of soldiers were returning with the condition.

Symptoms include memory loss, anxiety and depression. In 90% of cases they disappear within three months.

'Signature injury'

The Guardian reported that the Pentagon had designated mTBI as one of the "signature injuries" suffered by soldiers coming back from Iraq.

The MoD said it was collaborating with the US Army to investigate the condition, but a spokesman emphasised that it did not necessarily accept that the disorder was as widespread is it is believed to be by the Americans.

The spokesman said: "It is a very, very complex area. We have no way of knowing whether that [the US assessment] is accurate because there is a level of dispute as to what constitutes mTBI."

If the American figures are correct, this is massive. Absolutely massive

Kit Malia, cognitive rehabilitation therapist

He said symptoms may last for as little as 72 hours - and had gone in 80% of cases within two weeks, and in more than 90% of cases within three months.

The questionnaire-based self assessment is currently being trialled in Iraq and Afghanistan, and will be brought to all those who may be affected in the new year.

The questionnaires are supported by a helpline and a website, and there is an mTBI treatment programme at the military rehabilitation centre at Headley Court in Surrey.

The condition is caused by a blow to the head or by being close to an explosion. It can also be sustained in contact sports such as boxing or rugby.

Identification measures

The frequency of improvised explosive devices (IEDs), used as roadside bombs in Iraq and Afghanistan, has put soldiers who have served there at particular risk of the injury.

Shadow defence secretary Liam Fox welcomed the government's move to survey soldiers, but said the US was ahead of Britain in treating the condition and that measures to identify it were needed.

"I now understand the Defence Select Committee in the House of Commons will look into this as a matter of urgency and that I very much welcome."

Kit Malia, a cognitive rehabilitation therapist who will oversee the treatment programme, told The Guardian: "I think the issue is that we don't know whether the Americans are correct.

"But if the American figures are correct, this is massive. Absolutely massive."