Almost half of the service personnel assessed by military pyschiatrists had mental health issues that were not clearly linked to their career in the armed forces, or were “Walter Mitty” characters who fabricated their experience, according to a leading expert.

Ian Palmer, a former senior military psychiatrist who ran the government’s medical assessment programme (MAP), a veteran’s mental health service, found that in 42% of cases there was no definite link to military service and at least 10% appeared to be making up or significantly exaggerating their service history.

Palmer, the first tri-service professor of military psychiatry to armed forces, said the predictions of huge numbers of veterans suffering post-traumatic stress disorder (PTSD) following tours in Iraq and Afghanistan had failed to materialise, while various websites had made it easier for people to learn how to articulate symptoms.

“Fabrications are intriguing because they range from outright fraud through to the fantastic and even delusional. I reckon about 10%, which may be an underestimate, of those coming for assessment may have either exaggerated or fabricated,” he said.

Palmer said too many people, including health professionals, were quick to make a causal link between mental health and military service.

“Within society there seems to be an almost reflex desire to link health problems in veterans with their military service. Just because someone has served, it does not mean that their mental health problem is related to their service.”

Palmer’s comments coincide with a new study published in the Defence and Security Analysis journal that claims that some veterans embellish their military service because media scrutiny of PTSD associated with the Iraq and Afghanistan wars has led the British public to expect that most veterans had been traumatised by their tours of duty.

Hugh Milroy, the chief executive of the charity Veterans Aid and one of the study’s authors, said the volume of fabricated military careers they were uncovering was disquieting.

“The fabrication of service histories that don’t chime with reality and assignment of problems to fictitious traumatic events is disturbing, insulting to those whose experiences are genuine and causes us to waste time and money,” he said.

The phenomenon has allegedly become so widespread that an internet veterans’ group, the Walter Mitty Hunters Club, has been set up to expose cases.

Made up of more than 20 former and current members of the armed forces backed up by a wide network of supporters, the club tracks down civilian imposters they dub “Walter Mittys”. The group alleged last week that the military medals a Kent councillor claimed to have been awarded were bogus.

Currently there is no legal sanction against such deception in the UK. In the US, however, the unauthorised wear, manufacture or sale of any military decorations and medals is prohibited under the Stolen Valor Act.

Edgar Jones, a professor of the history of medicine and psychiatry at King’s College London, said the deception risked taking finite resources from deserving cases.

“The pressing issue of ‘stolen trauma’, that is the elaboration or falsification of traumatic experiences and the symptoms of post-traumatic stress disorder, is important because it has the potential to undermine the validity of genuine cases and dilute scarce resources.

“If the public begin to suspect the veracity of veterans with psychological disorders, it could reduce their willingness to give to military charities, whilse also increasing the stigma attached to mental illness.”

The MoD says it has improved improved mental health services for the military. The government committed £7.4m to the issue last year, alongside awareness campaigns such as “Don’t Bottle It Up.”

A report from Kings College London last year revealed that members of the UK armed forces are twice as likely to develop depression or anxiety than members of the general working population.