`Where do you think the stuff I do on the radio comes from?'

Don't wrack your brains too hard, people. Howard Stern, America's most intolerant shock-jock, already has the answer: trying too hard to be Mr Nice Guy. You don't buy that? Go see the movie.

Park Lane, inside the Dorchester Hotel. The room is alive with the murmur of sycophants. American shock-jock sensation Howard Stern is in London to promote Private Parts, the film version of the best-selling book of his life-story, in which he makes an acclaimed acting debut as himself. A female representative of one of Britain's interchangeable radio stations emerges from Stern's chamber, her 10 minutes up. "How did it go?" a colleague asks. "I let him feel my breasts!" she exclaims, before embarking on what would sound like a lengthy discussion of recent surgical procedures, if good manners didn't prohibit eavesdropping.

Persuading people that it is in their interest to expose themselves - physically as well as mentally - is Howard Stern's bread and butter. His radio career has been built on the proposition that a woman's value to a largely male listenership is inversely proportional to the number of clothes she has on. Yet his quarters seem like a haven of decorum after the hubbub of the ante-room. Monstrously tall and improbably good-looking - far from the self-confessed "uber-Geek" of pre-infamy - Stern debates the distinction between the incubus and the succubus. The former is a male demon who has sex with sleeping women, the latter a female demon who has sex with sleeping men. As a hairdresser fluffs up his luxurious curls for the benefit of the photographer, the possibility presents itself that this man might be incubus and succubus rolled into one.

On his two previous visits to the UK, things did not go quite so smoothly. One time, back in the Eighties, he was on a small stage singing with his friend Dee Snyder from Twisted Sister when a member of Sigue Sigue Sputnik threw a plate at them. On the other occasion, Howard was broadcasting from a pub and a woman got so annoyed with what he was saying that she climbed up over the partition to try and hit him. This, Stern observes in a voice as rich and satisfying as well-made Dundee cake, was "the funniest damn thing you've ever seen".

When the things he says make people angry, as they inevitably tend to (sample Stern insight from Private Parts the book, re Rodney King: "They beat all the ugly out of him, now he's a superstar"), does this make him happy or just bemused? "Oh, bemused definitely. Because to me words are just that - words. I love language. I would never get offended by words, only by actions. At this point, Howard cites the convenient example of one of his most prominent American Christian critics - who was recently picked up by the police on charges of child-molesting. "I'm like `Wow, that's great'. This guy's telling me what I should or shouldn't be saying while he is out there wrecking little kids lives.... "

Moral righteousness has always been one of the most favoured weapons in the Stern armoury: all the more deadly for its incongruity - this is the man who has uplifted the American listening public with such choice items as "Bestiality Dial-a-Date". He may delight in frolicking on the floor of his studio with semi-naked porn stars, but Howard Stern's licence expires the moment he leaves the studio. And virtue in this case has been its own reward: the unimpeachable respectability of Stern's family life with his wife and the three daughters he forbids to listen to his radio show has proved a priceless asset.

"It's not like I've only stayed with my wife because I want to say `Hey, fuck you' to everyone who thinks I'm a sleazebag," Howard insists chivalrously. "It's just interesting that this is the one thing they can't attack..." But he does consciously use his squeaky-clean domestic profile to wind people up? "Oh yes, sure. Absolutely." This will not come as news to those lucky enough to have caught Stern's memorable barbecueing of Chris Evans on last week's TFI Friday. Britain's most notorious Howard Stern-wannabe could have had a long-lasting marriage like his inspiration, Howard counselled, "but you had to go and be with all your sluts"

Reading Private Parts the book, which, for all it's determination to offend, is a compellingly honest and extremely funny piece of work, one might have expected Private Parts the movie to be the next step in the classic American lineage of Wayne's World, Jim Carrey's every move and Beavis & Butt-head Do America. (This is the tradition that people sometimes mistakenly refer to as dumbing down when what they really mean is smartening up.) That the film actually turns out to be a disconcertingly conventional rags-to-riches story in the mould of Rocky or the movie biography of Tammy Wynette is something of a disappointment. Stern says that among the 20 or so drafts of the script, several were more experimental than the one that finally got made, but insists that structural innovations such as a grown-up Howard visiting his own teenage self "didn't really come off". They sound like they might have been fun though.

It may be, however, that the true resonance of the Howard Stern story is in the real-life meat rather than the cinematic sandwich. How a son, "raised like a veal" by a mother who insisted on checking his temperature with a rectal thermometer every day till he turned 18, grew up to take the temperature of his nation on questions of private and public morality. How a young Jewish New Yorker, inspired by years of racially motivated schoolyard persecution and a radio-engineer father whose favourite term of endearment was "shut up you moron", developed a talent to abuse which could cut effortlessly across the lines of ethnic and generational diversity. Perhaps these are stories big enough to withstand conventional framing.

Is there an element of "I took it, so why shouldn't you" about it when Howard Stern is dishing out verbal abuse? "Probably yes. I guess the apple doesn't fall far from the tree."

How would he react to the criticism that the reason his radio show works is that he doesn't care what people listening think of him, whereas the problem with the film version of Private Parts is that it seems hell-bent on proving to the world that inside the callous shock-jock there is a decent human being struggling to get out? Stern nods animatedly. "But that's what I wanted it to be! The people who know me personally are always going `Man, you're such a good guy - how could you be that monster on the radio?' And that's why I didn't want to present that monstrous image in the film, because I wanted people to walk out of the cinema knowing that I do have the ability to step off the air and have a relationship with a woman or talk to my bosses on a very rational level."

Howard pauses for breath. "The sick part of it is that I hate that aspect of my life. It's all lies. It's in real life that I feel like I'm role- playing. It's only when I'm on the radio that I feel like I'm really me." So while a conventional bio-pic might seek to show the real man behind the public mask, Private Parts wants to show that the public mask is the real man, it's the home-loving private individual who is the despicable fake? "Where do you think the stuff I do on the radio comes from? All day I walk around with that shit locked in my head and I'm really controlling it. I can't even pick up the phone and complain to the phone company - I have my wife do that. It's only when I get on the air that I finally get to be the man that I am inside."

So while the conventional, lapsed liberal position on Howard Stern is that his are the dark impulses that lurk inside all of us, and even though the social consequences of airing these feelings on a daily basis may not be entirely beneficial, it would be more dangerous to bottle them up... Howard Stern's position on Howard Stern is that the man is truly evil and the world would be better off if he was in a Turkish prison? "That's right!" Howard leaps out of his seat in his excitement, all but head-butting his hairdresser in the process. "That is the correct assessment."

`Private Parts' goes on release tomorrow (see review on page 7)