Professor Jamie Hacker Hughes added that the 20% of military veterans who develop mental health problems face a postcode lottery of treatment.
Many of the UK's five million estimated former service personnel do not have access to adequate treatment services, said Prof Hacker Hughes, visiting professor of military psychological therapies at Anglia Ruskin University.
The problem is growing as an additional 24,000 people leave the Armed Forces each year.
The former head of defence clinical psychology at the MoD said: "There is a postcode lottery as to what service a veteran gets.
"There are lots of excellent services for veterans but not everyone has access to them. There are large areas of the country where they are no specialist mental health provisions."
Prof Hacker Hughes said a number of barriers restrict treatment including veterans not having access to the correct local services. He said some may feel GPs do not understand their experiences.
Research released last year shows that only half of those experiencing mental health problems sought help from the NHS.
Prof Hacker Hughes is calling for equity of services across the board. He said specialist centres that treat former troops should share their expertise.