Richard James, aka Aphex Twin, is the most inventive and influential figure in contemporary electronic music. He is also the most unpredictable. Which probably explains why he is so late for the interview. With a new 30-track album called Drukqs about to hit the shops, James, hardly your typical self-promoting pop star, turns up at the cafe inside London's ugly Elephant & Castle shopping precinct 21 hours after the interview was scheduled to start.

You would never guess from his flexible attitude towards time-keeping and scruffy appearance that James is a prodigiously gifted, not to mention hugely prolific, recording artist whose intensely strange and arrhythmic dance music has made him a millionaire, earned him accolades such as "the Mozart of techno" and had the likes of Madonna on the phone, imploring him to remix their songs.

Nor would you associate this friendly character with 1998's notorious, nightmarish Come to Daddy video, in which legions of midget Aphex Twins, satanic grins etched into their replica bearded faces, terrify passers-by, among them a frail OAP. As disturbing and viscerally impactful as pop promos get, Come to Viddy, as it was titled, positioned James - with more than a little help from cult director Chris Cunningham - as the Chris Morris of the electronica set. Something of a mutual appreciation society, Morris used Aphex music to soundtrack his recent E4 series, Jam, while James considers Morris "the best comedian of all time".

"He's amazing, that geezer," he says, his voice betraying his Cornish roots as well as traces of cockney. Morris and James have both done work that veers between radical and repulsive, but, he says, "I don't find any of his stuff offensive. A lot of my friends watch it with their hands over their mouths, like, 'God, that's so shocking.' I just find it normal. Every single person has twisted thoughts that they're just too scared to tell anyone about."

James is hardly backwards when it comes to revealing his own twisted thought processes. "The other day, I was lying in bed, stoned," he remembers. "I was thinking, 'What's the scariest thing you could think of?' And I ended up imagining people coming into my house and doing hideous things to me, tying me up, stripping me naked, and squirting this foam into my mouth and down my throat, shoving it up my nose, into my ears, jamming it into my tear ducts, until it all went solid. I was getting the Fear. I had to go, 'Think about something nice, you twat!'"

He's a nice boy, really. Although he has been known to polish off whole bottles of White Russian vodka "because they drank it in The Big Lebowski", during the interview he sticks to cappuccino and sparkling mineral water. He even rides a pushbike because if he bought a motorbike "my mum would disown me". Then again, he lives in a converted bank, and he owns a tank, which he parks outside his parents' home in Wales. And he recently bought a submarine.

"Loads of countries have ex-military gear that they want rid of," he explains. "Missiles, rockets - you can get all that shit. You could probably buy a battleship if you had enough money." How much was the sub? "About £40,000. They're really cheap." Can it be submerged? "Of course. It's totally pukka. You could live in it. It hasn't got any torpedoes," he says, suddenly forlorn. Then he brightens. "I was thinking of getting these rockets for my tank. Side-mounting missiles. Just think: thousands of pounds for just one push of the button."

Aphex Twin's weirdness has made him a wealthy man. Now 30, he put out his first record, Analogue Bubblebath, in 1991, although he had actually been making music, building his own synthesisers and writing his own computer programmes, in his bedroom from the age of 14, hence the title of his debut album, Selected Ambient Works 85-92. Today, his music, released either on the celebrated Warp label or on his own Rephlex imprint, is used in films and on TV adverts - and the name Aphex Twin is a byword for maverick genius.

He has worked with avant-garde composer Philip Glass. Extreme noise terrorists Limp Bizkit and Slipknot want to work with him. He was cited as a major influence behind Radiohead's decision to change musical direction. He's even remixed a forthcoming track for Craig David. "A total aggro thing," says James, "just to fuck him off."

Everyone loves Aphex Twin. Especially James. "It sounds really arrogant," he says, "but my music's my favourite music ever. I prefer it to anyone else's." He claims that his most innovative and original music will, however, remain unreleased, "because I don't want people ripping me off."

His fifth album as Aphex Twin - other aliases include AFX, Polygon Window, Caustic Window, Blue Calx, The Dice Man, GAK, Power-Pill and Q-Chastic - is the new double-CD, Drukqs, which ranges from exquisite blue mood piano meditations worthy of Debussy or Erik Satie to furious digital exercises that sound like pneumatic drills gone haywire. He doesn't have a strange dual personality, though - just "a low boredom threshold".

Nor was Drukqs made on drugs. "It's got nothing to do with it," he says. "It's just a word I made up." There are other made-up words used as song titles on Drukqs, such as jynweythek and bbydhyonchord, none of which are the result of experiments with hallucinogens. "I never wanted to big up any drugs, because I don't reckon they deserve it. It's just something that you choose to do. I probably come across as, like, 'Yeah, acid and weed are amazing.' But I don't think that at all, really. And if I did, I wouldn't want to say it in an interview. Plus, I'm never under the influence of drugs when I make music. Whenever I have been, it's always been totally rubbish. It's a real disciplined thing, making music. When you're tripping, you're just fucked. You could never get it together to make a track. When I'm stoned, I go to bed."

True enough, on Drukqs there are feats of micro-programming and virtuoso editing to make the mind boggle. But is this technique for technique's sake, a triumph of speed-prowess over content? "It's quite similar to guitar solos," he concedes, "only with programming you have to use your brain. The most important thing is that it should have some emotional effect on me, rather than just, 'Oh, that's really clever.' There's a lot of melancholy in my tracks." His best ones, he says, are those which evoke feelings that can't quite be described, where "you're not quite sure what emotion it is".

Whereas most white musicians these days are born of the blues and the Beatles, Aphex Twin's lineage is Stockhausen, John Cage, Kraftwerk, Brian Eno and the Detroit techno of Derrick May. James takes in his stride the fact that he is now considered as important as these all-time electronic greats. Even having Madonna on the blower didn't faze him. She rang him one day out of the blue at home because she wanted some of his strange magic to rub off on her: cool by proxy. Aphex had other ideas for the mooted collaboration.

"I wanted her to do these animal impressions," he says. "I had a whole list of them." But he changed his mind about working with her: "I'm not interested in doing it just to make millions, like a lot of other people. If I did it, that's all interviewers would have talked about for the rest of my career." He found Madonna's interest in him almost vampiric. "Her whole career's been like, 'Oh, they're the trendy person of the moment, I'll work with them to make me younger.' They're using you."

James may have monumental self-belief, but he has no illusions about the fate that awaited him had he not succeeded in the music business. Like Eno, he is self-taught. He builds, and plays, his own instruments, yet he has no training, whether technical or musical. If he doesn't know something, he reads a manual. "The best musicians or sound-artists are people who never considered themselves to be artists or musicians," he says. "I'm just some irritating, lying, ginger kid from Cornwall who should have been locked up in some youth detention centre. I just managed to escape and blag it into music."

And if he hadn't? "I'd have gone to jail for computer hacking. I was already getting into loads of trouble for that. I got suspended from school for hacking. It's so addictive, it's like gambling. I'm a really good hacker, but I'm not a sensible person, so I'd have got caught if I'd gone down those lines." Not that he needs the money now, with over a million in the bank. "I've been tempted," he smiles, "but, yeah, financially I'm all right."

Not surprisingly, considering its challenging, provocative style, Aphex Twin's music gets used a lot on TV whenever the subject is confrontational or disturbing. "It's always on programmes about surgery, or rapists, or paedophilia, or murder, or war," he says. "It's like, 'I'm glad that's how you see me!' But that's better than it being used on some cooking or DIY programme." It has been used on adverts for Pirelli and Orange - is there anything he wouldn't allow his music to advertise? "Only private health," he replies. "I've said no to that. If it's against my morals, I won't do it."

So he's a moral person? "Definitely. Everyone's got morals, even if the moral is, 'I believe in killing people.'" He doesn't agree with limiting yourself when it comes to art and self-expression. "There shouldn't be any censorship. I believe in protecting children from things - that's up to the parents. But I don't think everyone else should suffer just because there are irresponsible people out there." Don't artists have a responsibility to their audience? "No. You should totally do what you want to do." What about that poor old dear in the Come to Daddy video? She looked scared half to death! "She was an actor," he says, humouring the dim-witted reporter. "She was really wicked, and she loved every second of it. She couldn't stop talking about it over her pie and mash."

James describes himself as "a really well-balanced person". The media image of the demented raver who DJs with sandpaper discs "was made up because I didn't want to come across as average and boring". He has even thought about having kids, though not just yet: "I'm only terrifying to people who are nasty to me." The fact is, no one becomes this successful, this far-reachingly influential, by behaving like a loon. "You can't just make good art these days," is his parting bit of advice to all those Aphex wannabes out there. "You've got to be a good businessman. I'm good at psychology - I can see how to play certain situations. I'm a good chess player. You've got to recognise all the possibilities."

Drukqs is released by Warp on October 22.