For a start, despite its title, Girls is a book about men. Girls feature in it, of course, and even one or two women, but it is emphatically - you might even say obsessively - about the male of the species. It does not present them in a flattering light. In fact, it is one of those unsettlingly provocative or, depending on where you stand, unsettlingly honest books that, like Hanif Kureishi's Intimacy , may well make women won der if all men are, to some degree, like the men between these pages: predatory, amoral, ruthless in their pursuit of power and the often illicit pleasures that wealth and privilege afford them.

'If I was being truthful, I'd have to say I wrote the book so as not to end up like one of the guys in it,' says Kelman, laughing. 'I felt I had to understand what I had to avoid. I've just gotten engaged, but I do feel that the propensity to be utterly cynical and do whatever it takes to succeed is inside every man to one degree or another. It has something to do with the male drive to success, and the things people do to themselves, as well as others, in order to succeed. Though everyone picks up on the sex stuff, the book is not really about sex at all; it's about power.'

Sex, though, looms large in the narrative and is a big part of why the book has garnered headlines and already become a bestseller in both America and Italy. Elle magazine described it as, 'preternaturally poised, vastly literate, and sticky with sex... Girls is one of those books that gets its hooks in you from the first sentence.'

Nearly all the sex in the novel - and there is a lot of sex in it, often graphically described - is between adult men and pubescent girls. Girls, as one of the many male voices in the book elaborates, who have 'flat bellies and unsupported breasts and bony ankles', girls who, as the title of a contemporary bestselling porn magazine boasts, are 'barely legal'.

Intertwining seven narratives, not including the author's own ruminations on Homer, who, it seems, laid down the ground rules of sexual attraction in The Odyssey, Girls is a veritable torrent of illicit male desire. A merchant banker visiting Korea has wild, untrammelled sex with a pubescent call girl. He tries to feel bad about himself afterwards, but instead feels 'fucking fantastic. Reborn'. Another man and his girlfriend are guests of his best friend in a plush villa in St Barts. He repays his host's hospitality by bedding their teenage daughter. Again and again.

'It's really about men who give in,' says Kelman, who seems far too young and well-adjusted to have written such a gleefully misanthropic book. He was born, as his press release mysteriously puts it, in the early Seventies and looks like a well-groomed pop star rather than a serious literary author.

He may well have written one of those zeitgeist-defining books that homes in on some of the more disturbing aspects of our current cultural obsession with youth, materialism, and how adolescent sexuality is now almost exclusively defined by the unreal standards of MTV and Hollywood. Given the subject matter, and the current moral hysteria surrounding real and perceived paedophilia, the book may well court controversy when published in Britain next month.

'I hope not,' says Kelman, looking slightly worried, 'because it is so obviously not a book about paedophiles. That's a whole different issue. It's not about underage sex, or even sex at all. Technically, all the girls in the book are legal. They are young women, they are not children. Many of them are precociously sexual and some of them are predatory, too. No one comes out of the book that well.'

Kelman initially wrote Girls as his college thesis while studying creative writing at Brown University. His CV, which is on display at his website - www.girlsbook.com - also includes a degree in brain and cognitive sciences at Massachusetts Institute of Technology, where Chomsky teaches. His father is a documentary director and Kelman worked in independent film before turning to novel writing. His mother is English and, as a child, he spent every summer in Dorset, before the family moved from New York to Rye in east Sussex, when he was 12. 'I attended boarding school there,' he says. 'It's where I get my ingrained pessimism.'

The book is indeed pessimistic, but it has the cold, hard ring of truth about it. Its overlapping narratives construct a composite of a certain kind of identifiable male psyche, which, he says, arose out of close observation of his more materially driven contemporaries.

'I had a close friend who was involved in the technology boom and made an absolute fortune almost overnight,' he elaborates. 'Every time I saw him, he seemed to have a new girlfriend on his arm, and each girl was always younger than the one before. It was just interesting to see how his relationship with women had changed because all of a sudden he was wealthy.'

In the book, this friend is captured in a telling vignette. 'I saw him at this new year's party,' continues Kelman, 'and he was with this girl who was about 10 years his junior. Here's this really cynical guy, and he's wearing a ring that said, "Dream More". I was like, "What?". I just went home and wrote the encounter down as a couple of sentences, and then I started seeing it everywhere and I just kept writing.'

That initial fragment of observation now nestles amid a welter of narratives that makes Girls a risky book formally as well as in terms of its subject matter. In places, it could be accused of parading the kind of 'look at me' cleverness that afflicts many postgrad novels - Adam Thirlwell's Politics springs to mind - not least in its many nods to Homer and Virgil. Whole tracts of The Odyssey and The Iliad are quoted, alongside Kelman's many meditations on the words we men use to describe - and deride - women. They make for provocative reading in their own right, but do tend to interrupt the pace of the other fictional narratives.

'Oh, I had to use Homer,' he says defiantly. 'I mean, I was going to bring in Shakespeare and Anglo-Saxon poetry, and various other literary works that dealt with the subject of sex and power, but it's really all there in Homer. The first Western narrative and it's about two men fighting over a girl. It's not even about Helen at all; it's about the rage of Achilles. And what is he angry about? He's mad because he's had his 14-year-old girlfriend stolen. I mean, how could I leave that out?'

More provocatively still, Kelman has one of his male narrators take a pop at Nabokov, whose great and disturbing masterpiece, Lolita , looms large here. At one point, a mocking male voice asks: 'Ah, Nabokov, why did Quilty have to pay? It wasn't a movie of the week, you didn't have to worry about the advertisers pulling out. And you must have known the Quiltys of the world never pay. So why did you do that, you coward, you pussy, you?'

I wondered if Kelman had second-guessed how the book would be constantly compared to Lolita and taken steps to counter that in the narrative.

'In a way, maybe, but it was more a philosophical question,' says Kelman. 'I kept thinking about Lolita after I started writing, and these questions kept cropping up. Nabokov makes sure Lolita is pubescent and not prepubescent, when she loses her virginity, and he makes Quilty pay for what he has done. I kept wondering whether that just some kind of lingering Victorian moralism on Nabokov's behalf, because, in the real world, that's not what happens. People do get away with it. Then again, the book is a masterpiece and you can only be so far ahead of your time.'

In Kelman's book, the men do tend to get away with it. Protected by wealth and power, they indulge their desires and seldom question the consequences. Except that the price they pay is evident in their very tone of voice, in their self-imposed detachment from the ideals of duty, loyalty and tenderness that underpin successful human relationships, in the sense that they have surrendered some irretrievable part of themselves without knowing quite how or why.

For all its delineating of transgression, Girls is a remarkably thought-provoking, even a political, book, and moves with unerring subtlety through the moral timebombs it ignites. It links this male compulsion to transgress with very young girls to the dynamics of the corporate market place, and also links a certain kind of misogynist thinking to the mindset of a certain kind of male power. As Kelman insists, it is not a book about sex at all, but one about power.

'I'm really interested in the age-old question of how power changes people, makes them harder, more cynical,' he says. 'It's about that conflict between youthful idealism and the cynicism that often attends adulthood, about getting caught up in doing whatever it takes to succeed. These are not evil guys doing evil things, they are ordinary guys who sacrifice a part of themselves, or their beliefs, in order to stay afloat in a combative male world. But as soon as they ditch their youthful ideals, something else happens to them; they lose their way in every way when they give in to their appetites.'

Intriguingly, the book begins with the question: 'How did they get so young?' and ends with the question: 'How did we get so ugly?'

Which, of course, is essentially the same question. 'You got it,' smiles Kelman, 'and, more importantly, it's a question I don't really answer. There are no answers in the book, only an exploration of those kind of questions. Essentially, I'm trying to explore the hypocrisy of so-called civilised behaviour. It's not about an us and them, they are all us. It doesn't spare anyone - not men, not women, not me, nor you.'