Authors say finding raises questions over how men who have served in armed forces are supported back in UK

Young British men who have served in the armed forces are three times more likely to have been convicted of violent offences than their civilian peers, according to a study published on Friday.

The report in the Lancet, the first to marry the experiences of almost 14,000 military personnel with details on the Police National Computer, also shows how troops who have been in combat are more likely to be involved in violent offending back in the UK.

The study's authors believe this raises questions about how the military and the NHS supports serving and former troops, some of whom end up abusing alcohol or developing severe mental health illnesses following tours in Iraq and Afghanistan.

Drawing on a random sample of 13,856 serving and ex-personnel mostly from the army, researchers from King's College London looked at criminal offending rates and the possible links between them and post-traumatic stress disorder, anxiety, depression and other mood disorders.

The study found that of 2,700 men serving in the armed forces under the age of 30, 20.6% had been convicted of a violent offence, compared with 6.7% in the general population. Men who had seen combat in Iraq and Afghanistan were 53% more likely to commit a violent offence than those in non-frontline roles. And personnel who had multiple experiences of combat had a 70% to 80% greater risk of being convicted of acts of violence.

Violent offences covered a broad range of acts, from verbal harassment to homicide. They did not include incidents of domestic violence [see footnote].

"More frequent exposure to traumatic events during deployment increased the risk of violent offending," the report says. "We noted a strong link between PTSD and violent offending. Combat veterans with PTSD and other mental health concerns frequently present with problems of anger and aggression." However, it also notes that troops who volunteer and are trained for fighting are not chosen randomly.

"In the UK, infantry units have traditionally promoted aggression as a desirable trait and such units frequently recruit individuals who are socially disadvantaged and are likely to have low educational attainment."

Dr Deirdre MacManus, who led the study, said: "Our study found that violent offending was most common among young men from the lower ranks of the army and was strongly associated with a history of violent offending before joining the military. Serving in a combat role and traumatic experiences on deployment also increased the risk of violent behaviour."

Prof Sir Simon Wessely, who co-authored the study, added: "We are suggesting there is a problem that needs to be looked at, but just as with post traumatic stress disorder this is not a common outcome in military populations."

Screening within the armed forces to identify at-risk individuals would not work, he argued. For every correct prediction there were likely to be five that were wrong.

Dr Walter Busuttil, director of medical services at Combat Stress, said: "These findings will help us to identify which veterans are most vulnerable and in need of appropriate care and treatment after leaving the armed forces. We are planning courses for anger management and domestic violence. We are about to establish programmes that deal with alcohol abuse linked to PTSD.

"It would be grossly unfair and inaccurate to characterise all veterans living with PTSD as potential criminals. As noted in the report the vast majority [83%] of serving and ex-serving UK military personnel do not have any sort of criminal record, and the likelihood of violent behaviour is lower among older veterans [aged over 45] than in the general population. What we require now is continued public education to reduce any negative connotations with seeking help for mental health issues, as well as sustained funding for services for veterans."

The Ministry of Defence has introduced a series of initiatives to encourage serving personnel to come forward if they fear they might be suffering from trauma or the early stages of anxiety or depressive illness, and has committed £7m to improve support services.

• This footnote was appended on 22 March 2013. The authors of the report have asked us to make clear that offences of domestic violence were not excluded. They are included in the violent offences category as offences such as assault. They were not identified specifically as offences of domestic violence because domestic violence is not a separate offence category on the Police National Computer Database.