“The first time I killed a lad,” says Andy McNab, “it was 1979, I was with the Green Jackets in Northern Ireland, I was 19, and he wasn’t far away, I could see his eyes. I was absolutely sh****** myself. But you can’t say you were scared.” Did he talk to anyone about his feelings? “Absolutely not. It wasn’t the done thing, you’re worried about peer pressure and promotion and being down as a fruit. Besides, nobody wants to know about any failings, it’s a success, it’s what you do. It says in the manual, ‘The role of the infantry is to close with and destroy the enemy.’ The Army calls it ‘being kinetic’, which means blowing things up and killing people.”

When McNab passed selection for the Special Air Service in 1984, there was, he says, among his new elite comrades, more honesty regarding the dangers of combat. “You’re older and more confident, so you do talk about it more, mainly, ‘F*** that, I don’t want to do that again.’ But there was no system, no counselling, although a couple of lads used to sneak off to a charity in Wales for help. Delta Force [the US equivalent of the SAS] used to have an in-house psychologist. We would take the p***, but actually, it was a good idea.”

After McNab led Bravo Two Zero, the SAS patrol behind enemy lines during the first Gulf War which later gave rise to his 1994 bestseller, he had a couple of sessions back in Hereford with Dr Gordon Turnbull. “His claim to fame was he’d looked after the mountain rescue teams who were at Lockerbie. He talked to us about post-traumatic stress, what the symptoms were and so on. At the time I didn’t think I got a lot out of it.”

But as McNab has grown older (he is now 48) and wiser, he has become fully converted to the idea that some, not all, soldiers suffer post-traumatic stress and need help. His new book, his first work of non-fiction (many novels have intervened) since Immediate Action, the sequel to Bravo Two Zero, deals with the consequences of such stress on several of his former SAS colleagues, the members of Seven Troop of the book’s title. In particular, McNab tells the story of Frank Collins and Charles “Nish” Bruce, both of whom committed suicide several years after leaving the regiment, in 1998 and 2002 respectively.

The catalyst for the mental deterioration of both men seems to have been the death of their colleague Al Slater at the hands of the IRA in Co Fermanagh in 1984. Collins and Bruce (and McNab) were present the night Slater was shot. But whereas Collins blamed his superiors for his mate’s death, and Bruce blamed himself, McNab didn’t blame anyone. “It’s not a science,” says McNab, standing at Slater’s grave in the SAS plot in St Martin’s Church, Hereford. “It was foggy, we couldn’t see ten feet, we had no comms, you make the best decision you can make at the time.”

He walks further along the row. All the graves have flowers on them, some have bottles of beer or wine too. Another friend, Paul Hill, “Hillbilly”, is buried here. He died on a covert operation in Cambodia in 1988. And here are Bob Consiglio and Vince Phillips, two of the three members of Bravo Two Zero who perished in Iraq in 1991. How does McNab feel, being here? “Just that they’re dead, and obviously it’d be better if they weren’t. But it’s all part and parcel of it.” McNab may sound callous, but what is there to say? But for pure luck, a bullet on a marginally different trajectory, and one of these men would be pouring a tot of rum on his grave rather than the other way around.

Nish Bruce is not buried in this churchyard. Frank Collins is, but not in the SAS plot, because he was not a serving member when he died. “The thing about Nish and Frank,” says McNab, “is they thought about it all too much.” He doesn’t think they were more intelligent, or introverted, or indeed extroverted, than others, but they were probably more sensitive, more likely to dwell.

“My wife reckons I’m all right because I only ever think about the next three hours,” says McNab. He isn’t joking. “Today’s today. If it works it works, if it doesn’t it doesn’t. You control what you can and the rest, f*** it.”

McNab believes both his friends suffered from post-traumatic stress, yet their condition was more complicated than guilt over Slater’s death or clichéd flashbacks to other battlefield horrors. Both men were involved in the SAS siege of the Iranian embassy in 1980. Both served in the Falklands war. Bruce told McNab he felt guilty about “killing a young [wounded] Argentinian lad, he’s dying, it was like a mercy killing”. And yet, says McNab, their real problems began when they left the forces. Indeed, “post-career anticlimax” may pose as big a problem for ex-soldiers as post-traumatic stress.

“From the day he left, Frank regretted getting out, but he couldn’t admit it. He was always looking for something, but everything was a disappointment.” Collins found religion, becoming an ordained Anglican priest, wrote a book, then asphyxiated himself with exhaust fumes in a friend’s garage. Bruce threw himself, literally, into skydiving, and then one day opted to jump out of a Cessna 5,000ft over Oxfordshire without his parachute. “I hope he was smiling all the way in,” says McNab.

Neither had prepared properly for leaving the Army’s embrace, but that itself is common. “Blokes know it’s coming but they ignore it,” says McNab. “They don’t realise the military is a tribe, a little clan that nobody understands, a very small part of our culture, and once you’re out nobody gives a f***. People don’t understand your language, your humour.”

McNab has studied the problems faced by ex-servicemen. They are massively over-represented among the homeless, in prison, in the divorce courts, among alcoholics and in the suicide statistics. Besides Bruce and Collins, two of his other close-ish colleagues have also killed themselves, and another tried to. “We’re not dropping like flies, but it’s well above average.” Several years ago, it was discovered that the number of Falklands veterans who have killed themselves far exceeded the number killed in the actual conflict (more than 400 as against 255). When an ex-serviceman takes his own life, the average length of time between his doing so and having left the Forces is 13 years.

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