As many as 9,000 Gulf war veterans believe they have Gulf war syndrome, even though research has never been able to identify what the condition is, a study shows today.

A study of British servicemen involved in the 1991 conflict has revealed that 17.3 per cent think they have the syndrome, regarded as a disabling illness resulting in fatigue, depression, and muscle aches and pains.

However, earlier research has shown it is impossible to identify any specific illness that could be called "Gulf war syndrome" or any specific cause.

Although Gulf war veterans suffered higher levels of illness than those who served in Bosnia or remained at home in the UK, the illnesses ranged from mild fatigue and headaches to severe urinary and sexual problems.

The finding is the latest from the Gulf War Research Unit at Guy's, King's College and St Thomas's School of Medicine in London. Questionnaires were sent to 4,250 Gulf war veterans, of whom 2,961 responded (70 per cent). Of these 513 believed they had Gulf war syndrome. If the sample is representative, it implies that 9,000 of 53,000 British service personnel believe they have the syndrome.

Writing in the British Medical Journal, the researchers say that the veterans' beliefs about their illness are important for their clinical care and for future programmes intended to protect against the threat of chemical and biological warfare.

They suggest the beliefs may have been transmitted from one soldier to another, like an infection, because of the army's "buddy" system, whichfosters close-knit groups.

"Concern over one's health may lead a person to seek support from peers ... As a result, a system of beliefs around the illness in which the veterans shared ideas about the nature and cause of their symptoms may have evolved," the researchers said.