Sebastian Horsley: He likes to shock with hookers, drugs and guns but who is the man behind the myth?

He once crucified himself in the name of art. But then the self-confessed rake, whose memoir is published this week, loves to shock – whether it's injecting lovers with heroin, spending £100,000 on prostitutes, or even waving a loaded gun in the face of an unsuspecting journalist...

The first time I saw Sebastian Horsley was a few years ago at a funeral. He arrived wearing a black frock coat, platform boots and eyeliner, with a well-known glamour model weeping on his arm. He wasn't actually trying to upstage the deceased – it was Willie Donaldson, a man he loved – but as we sang "Drop Thy Still Dews of Quietness", I peered across the chapel at this huge, pale, shock-haired, haunted figure, half-Dickens grotesque, half-matinee idol and wondered: who is that man?

A delinquent dandy. A posturing peacock. A junkie (reformed) and brothel-botherer (unreformed). A man who claims to have spent £100,000 on prostitutes: a libertine to some, a pervert to others. Preposterous to everyone. Especially himself. "I am half-Byronic, half-moronic; part-shaman, part-showman," he wrote me in an email (he likes to polish his epigrams as thoroughly as his shoes). "Half-Nazi, half-Liberace." The day I interviewed him I got a bit of both. He went prancing about his Soho flat in a red sequin suit, waving a loaded pistol in my face. Yes, a real Colt 38. Ruby Wax only had a banana pulled at her by OJ Simpson. Eat your heart out, Ruby. I'm delighted to say things got even worse after he put the gun down. Perhaps he was just a little over-tired and emotional. Finished copies of his autobiography had arrived the night before and he hadn't slept a wink from excitement.

Horsley's book is tipped for success, which rather panics him. He has always been an heroic failure. First he was a failed abortion. As he puts it, he hurtled to earth like a meteorite – even the pills his father gave his mother couldn't stop him – and exploded in Hull 44 years ago. "I was so appalled I couldn't speak for two years."

His first hero was Marc Bolan. So he became a musician. The fact he couldn't play was mere detail. The scion of the wealthy Northern Foods distribution dynasty, he paid to make several singles. They sounded, he says, like " an unsavoury stench in the ear", and were deleted by popular demand.

Next he became an artist. Not that he thought he could paint. When he came home one day to find burglars had taken everything but his canvases, he applauded their good taste. He was always better at being art than creating it. His masterstroke was being crucified in the Philippines in 2000. Like Damien Hirst's shark, it was good enough to get into the tabloids. "Art Freak Crucifies Himself" ran the headline. Fellow artist Sarah Lucas filmed the event and Gavin Rossdale of rock band Bush provided a soundtrack.

But he even failed at being crucified: he fell off the cross. The footrest gave under the weight of his atheist body. Is there a God or am I too fat? he wondered.

So he tells me during our epic, rambling, X-rated interview one sunny day in Soho. I find him sitting at an outside table on Meard Street (his perfect address – Shit Lane!), squinting in the sunshine like a recently disinterred Dirk Bogarde. He is wearing a cream three-piece suit, pink Turnbull and Asser shirt, and houndstooth check tie. His fingernails are painted pink. "Darling! Have you read my book? Can you tell me what it's about?" '

Dandy in the Underworld is a compulsive autobiography that tells the blackest truths in the jauntiest tone. Last week, one national newspaper called it "one of the funniest, strangest and most revolting memoirs ever written". Next week, if the Catholic Herald denounces it, Horsley's joy will be complete. The journalist Cosmo Landesman's wife vomited while reading it, he tells me gladly. "That's as good as a standing ovation."

His only fear is – he makes a Munch's Scream pose – Jimmy Boyle. Scotland's notorious gangster (now turned sculptor and novelist) may not take kindly to his revelations about their passionate affair. "If I happen to disappear in a strange gardening accident, given I don't have a garden – you'll know what's happened..."

He often ends sentences like this with a hysterical giggle-gasp. It's catching. On the tape recorder we sound like a pair of baboons."I live my life like an open book, even though it's open on the wrong page. It's amazing I was commissioned to write my autobiography at all. I'd never written anything except for cheques and suicide notes." (This isn't true. He wrote a column, "Sewer Life", for The Erotic Review for six years, and was briefly sex columnist for The Observer – until a column about anal intercourse printed on Easter Sunday drew record complaints, and he was sacked.)

His book's trajectory has been troubled, nevertheless. It's taken five years and two publishing houses. "When I delivered it to 4th Estate I was fired and all my dreams were broken. It would be nice to think it was because the book was so depraved and misogynistic, but I think the truth is they probably thought I was difficult. And why be difficult when you can be impossible? I shot up in the loos at 4th Estate before going into the meeting." .....................

He was paid the full advance and told to go away, "like the Sex Pistols". Then he found a new editor, Jocasta Brownlee at Sceptre. "She helped enormously. If I'd had my way, the book would have been like being trapped in a lift with a psychopath." As it is, it's more like being whispered a bedtime story by a psychopath. Assistance also came from his ex-girlfriend, Rachel Campbell-Johnson, an arts writer at The Times. (She is Rachel One; his other inamorata, glamour model Rachel Garley, is Rachel Two.) For someone who is often called a misogynist, he likes a lot of women. His good female friends include the artist Maggi Hambling and journalist Rowan Pelling. The book contains a few shockers – lines about pregnant women being as offensive as terrorists and the like – but the only woman who really suffers is Debbie, whose throat he slits. Debbie is a blow-up doll.

"Let's just say I am a misogynist. So what? We live in a culture where everybody's got to like everything. Well, NO!" He turns on that matinee-idol charm. "Shall we go up to my flat, darling? I think we should do the interview in bed."

Every sitting room needs a centrepiece, and chez Horsley, it's a wall of skulls. He picked a few up during his St Martin's days – thrown out for forging his grant papers, he left with several heads and an arm in lieu of a degree. On his walls are prized pictures from magazines, mostly of himself but some of dismembered bodies: a corpse on a train track, a leg destroyed by a shark bite. In his tiny loo there is some light relief: a picture of the crucifixion. Not his. Christ's.

Time for the prim questions. I ask what he will say if people accuse his book of glamorising drug abuse? "Good! People should be allowed to go to hell in which ever way they choose. It's not about good or evil to me. It's about witty or boring. Some people stay on the shore, some people swim out to sea. You want me to be a lifeguard? Fuck off!"

There's a chilling passage in the book where he injects Rachel Two with heroin. It's her first time. Defensible? "Well, she did ask me to for a long time, and..." his voice goes small. "There's something very beautiful about injecting someone you love with drugs..." Really? " Yeah..." He bounds like Tigger to the fireplace where a box of needles sits. "Wanna try?"

Don't worry, reader: he's been clean for five years. The needles are for his forthcoming art exhibition.

For all his talk of romantic nihilism, though, none of us lives outside morality. He says he still visits brothels. "Yes, three days ago. A gentleman should make love a good deal, and £25 is a good deal." Well, what if he suspected one of the women was working there against her will, or had been trafficked? "Oh I wouldn't go along with that," he scoffs. "I do have some standards. I may be a cannibal but I do say grace. People who have a reputation for being evil are usually good. It's all those Mother Theresa Save the World knobheads you have to watch out for."

He has disappeared into his kitchen and is fumbling in his fridge. It's almost entirely empty. Like Gilbert and George, he eats out every day. So what's he up to?

"Sorry, darling, it's too embarrassing. It's just an OCD thing I have to do. I get it into my head that if I don't do it everything will be awful." He leaps back into the room and looks at me with terrified brown eyes. " I have a philosophy of leading my life like an open book, even though it's open on the wrong page."

Dear Sebastian, you've said that before. In fact everything he has said today he has said before. The lifeguard metaphor, the cannibal quip... " I don't speak, I quote. I am a fraud. I have cobbled together my personality from hundreds of little bits. I am simultaneously the most genuine and the most artificial person you will ever meet."

Is there, for him, a comfort in repeating the same phrase? A sort of linguistic OCD? "Ach, yes! You don't object to hearing Beethoven's 9th on grounds you've heard it before, do you? There are times when I hear things coming out of my face and I think, 'Oh God, you hardly change your parrot cries' – but I'm always writing new material. I was writing new material only this morning..." Horsley doesn't speak; he delivers lines he has written for himself. No wonder his life is like a play – and what's this? He's changing costume?

The dandy has disappeared into his bedroom and is rustling about. He opens the door to reveal himself resplendent in a red sequin suit, Shirley Bassey via Savile Row. "Come in, my darling!" The bedroom is also dark and and wooden, hung with red velvet and empty gilt frames.

"What are you afraid of, darling? Are you more afraid of death or growing unattractive?"

"I'm not afraid of anything," I retort.

"Don't give me that crap!" he laughs. "I'm going to get out my gun and shoot you in the knee!"

He reaches for the Colt 38 that sits on a velvet pillow beside his bed. I duck down instinctively behind the bed, giggling nervously. I've read his memoir. I know it's loaded and that a prostitute once nearly let it off in his face.

"Yes she did. Look, here's the mark the bullet made." Indeed, there's a gash in the brass coatrail. Now his ageless Peter Pan face is looming closer – he's trying to kiss me.

"Oh, I really enjoyed that when you pushed me away," he says. "You can't come to Horsley's house and not be seduced."

Reader, I could. But though I was not literally seduced, metaphorically I succumbed. This dandy is a world of fun.

"Bring your boyfriend to my book launch, darling!" he cried after me. "It'll be like bringing a pot noodle to a banquet." *

'Dandy In the Underworld: Hookers, Dealers, Tailors' is published by Sceptre, £12.99