The good news is that Irvine Welsh, having been obliged to give the subject some thought, does not believe that all men are potential paedophiles. What he does find interesting is that advertising and the mainstream media pander to a perceived tendency in men to respond to images of females captured on the cusp of puberty.

Welsh is the Scottish writer who shot to fame in 1993 with his first novel, Trainspotting, a surprising, not least to himself, massive worldwide bestseller about a group of Edinburgh junkies mostly written in dialect. The arresting opening line – “The sweat wis lashing ofay Sick Boy; he wis trembling” – has been quoted so often it has become youth culture’s equivalent of “It was the best of times, it was the worst of times”, but the book was also celebrated by the likes of such august critics and academics as John Carey, emeritus professor of English literature at Oxford University. Three years later, Trainspotting was made into a film directed by Danny Boyle, launching Ewan McGregor’s career and further boosting the author’s.

Novels have been released since then, some with short titles: Ecstasy, Filth, Glue, Porno; others with a few more words, among them The Bedroom Secrets of the Master Chefs and If You Liked School, You’ll Love Work. The new novel reverts to the school of short titles – Crime – and deals with large themes of retribution, redemption, abuse and male anxiety, seen through the horrid prism of paedophilia.

The central character, Ray Lennox, is a Scottish cop who has had a breakdown while on the trail of a serial killer of female children. In the course of his investigation, interviewing relatives of the latest disappeared girl, Britney (named, doubtless, after the singer who dressed up as a schoolgirl for her first hit song), he experiences the full weight of his colleagues’ disapproval of the chain-smoking single mother and the assumption that she must be partly to blame.

This whole subject (including the blame-the-mother syndrome) is discomfitingly topical – from Portugal, with the vanishing of Madeleine McCann, to Goa (the murder of 15-year-old Scarlett Keeling) and the ongoing morbid fascination with the Austrian captivity cases of Natascha Kampusch and Elisabeth Fritzl.

The obvious question is whether Welsh found himself besieged by inappropriate thoughts when researching the book. “In order to write something like this, you have to feel pretty confident in your own sexuality and be in an almost unimpeachable state as regards that because if you didn’t, I don’t think you could physically go through that kind of journey,” he says. “One of the things I wouldn’t do is any research at all on the internet because I have no interest in getting into paedophiles’ websites. The idea was quite sickening to me. There’s so much shady stuff in my life in other ways that I had to be content that there was nothing of that sort in my inner workings.”

Welsh was helped by police officers and social workers in the States who briefed him on how organised paedophile rings work. He also read a great number of academic and clinical psychology texts and spoke to survivors of childhood sexual abuse.

The narrative switches from the unravelling of the Britney case in Edinburgh to Miami Beach, where the cop is on holiday with his fiancé trying to wean himself off anti-depressants. Behind this haunting are hints of something murky in Lennox’s past. Unable to heal himself in the sunshine, Lennox, a recovering addict, demolishes himself in a bar, is picked up by a pair of predatory women, goes on a cocaine binge and flees with a ten-year-old girl (the daughter of one of the women) who has been the prey of a paedophile ring.

Welsh is not comfortable with the idea that he has become some sort of instant expert on paedophilia and, indeed, the more he delved into the subject, the less clear cut it became to him. “The currents of sexuality run deep and they’re very confused. Advertising, for instance, seems implicitly to believe that there is this kind of paedophile locked in the male sexuality – the way that very, very young women are made to look even younger. Some kids seem highly sexualised from an early age and they obviously need to be protected from themselves. What is really disturbing about paedophiles is the God-like status they assume… the calculation, the long-term grooming, the idea that it’s society that is at fault and therefore they can break the rules.”

One surprise for him was how very differently people respond to abuse. “Some women can have experienced something quite minor – ‘I was touched up by my uncle’ – and it can absolutely devastate and wreck their lives. And there are other people who were kidnapped as children, serially raped and cult stuff like that and yet they seem to be coping and functioning quite well.” Here one thinks of Natascha Kampusch, who was held captive in a tiny space from the age of 10 to 18 and seems mystifyingly self-composed to many commentators. She, in turn, is angered by the idea that she must play the victim to validate other people’s expectations. “What we don’t know is how much not talking about it or repressing it is as much a coping mechanism as talking about it,” Welsh says.

He had started writing a good six months before the McCann case but after the news broke he felt unable to continue for a while: “It was just so kind of big and so horrible and obviously, like everybody else, I was distressed. I thought, ‘Should I really be writing about this?’ But the reason why I went back to it is that the story is very different and the initial draft was looking at why the guy [Lennox] is the way he is. And how when you read about a paedophile case, everybody starts seeing paedophiles everywhere – and also how appropriate is it, anyway, for adults to be around kids they have no relationship to?”

The initial catalyst for the book was something that had taken place in the writer’s own life – when a friend of 20-odd years’ standing broke down and wept in a pub, saying that he’d been abused by a close family member that Welsh and his friends all knew. “Within our Scottish working-class male culture, we were singularly unequipped to deal with it,” he says. “Our first reaction was wanting to kill the abuser, basically. But there was also a kind of loathing for this guy – not so much the fact that he might have brought it on himself but that he had involved us in this thing. So I wanted to work out these ideas of compassion and rehabilitation and retribution and what happens when you keep something to yourself for so long.”

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