Donna Mahoney’s husband Peter had always wanted to be a soldier. But from the start, she had said no. He would be away too often. They had been married for 21 years, childhood sweethearts, and she wanted a family man. So they compromised. She said he could be a part-time soldier, and in 1996 he joined the Territorial Army (TA).

From then on, for 19 days once a year, he put his uniform on and went off, in her words, “to play with guns”.

Then one morning in early March 2003, a brown envelope dropped through the letter box of their home in Carlisle. It was marked “On Her Majesty’s Service” and 10 days later Peter was off to Iraq, attached to the Royal Logistic Corps. Donna was in shock.

“When he got the call I felt sick. I thought that at 45 he’d be too old to go to war. Then I saw it all happening on television and I was gutted. I went to the army office and told them I hadn’t heard from Peter . . . that he’d promised to call. They told me that no news was good news and I should go home and pray. So I did and started on a bottle of vodka.”

The going away, as anyone who has ever been to war will tell you, is not half as bad as coming back. And if you’re in the TA, it is doubly bad, as research, published on The Lancet’s website last week, confirms. Reservists returning home from active duty in Iraq were found to suffer much more psychologically than the regular soldiers they had fought alongside: they were 50% more likely to have what we now call post-traumatic stress disorder (PTSD).

There is a consensus that combat itself is not the prime cause, not the old-fashioned shell shock. But reservists are apt to take the anxieties of home life to war with them, worrying about the family, the job they might lose, the loss of earnings. And after months on active duty, having knit in with a unit and feeling part of the regimental family, the prospect of returning to normality, to the comparatively dull routine of civilian life, is often daunting.

Since the end of the cold war, both the regular army and the territorials have been pared down. But conversely, the demands on the TA have increased, and by so much that its 35,000 members now make up 25% of the British Army.

When the war in Iraq began three years ago, around 4,000 territorials were sent to fight there. They made up 10% of the entire British fighting force, and that quickly rose to 20% as the war progressed. Since then, some 10,000 of them have served in Iraq with 600 still there now.

When I was in Basra a few months ago, I met many of them, men and women from all walks of life: teachers, accountants, plumbers. You would not know they were reservists until they told you, because they are sworn in as regulars while on active duty and wear no identifying insignia. They told me it takes time for the regulars in a unit to accept them and new arrivals are nicknamed “stabs” — stupid TA bastards.

However, once they have proven their worth, whether fighting from the same foxhole or nursing the wounded in a field hospital, they become one and the same. When that happens, they told me, the camaraderie they share with the regulars is unique, a special something they take back with them on their return to Blighty.

But some homecomers unknowingly carry back hidden demons that haunt and torment them. Like Donna Mahoney’s Peter.

“When he came home from Iraq he looked great, all brown, really fit. He was gorgeous. Our children, we’ve got four of them, put up ‘Welcome Home’ banners on the house, ribbons and things and he was really chuffed. He seemed quite normal and it was really, really lovely. But within a few weeks it all began to change.”

When the first wounded territorials began coming back from Iraq, both the army and the Ministry of Defence seemed surprised, as if it was unexpected. It was even more shocking for the wounded part-timers, who having done their bit for Queen and country, discovered they were not eligible for the same medical treatment as the regulars. They were civilians again and that meant the NHS.