ACCORDING to the theory, the truly innovative science fiction writer must live in the suburbs of reality, the far flung satellite towns of reason, commuting back and forth to source his starry fictions. Iain M. Banks, however, does not hold with this Mary Shelley derived notion of madness becoming the muse.

"I just pick up my stories as I amble along, little bits of this, little bits of that. It gets easier the longer you've been at it."

Now 47, Banks is a beardic, cheery sort of character, bringing to mind a peculiarly amiable geography teacher. He emerged in 1984 (as plain Iain Banks) with The Wasp Factory, a twisted and gnarly narrative of a murderous adolescent and his gruesome preoccupations. It enjoyed enormous success, instantly attracting cult classic status.

He's been publishing a book a year since, sometimes science fiction (with the "M" added to his handle), sometimes mainstream. They sell by the truckload and are usually greeted with almost orgasmic critical acclaim. It's a merry position for this least dour of Scots.

"Aye, I mean I have it completely sorted really, don't I? (Much raucous, cat who got the cream laughter.) To an extent, I have two separate audiences, there doesn't seem to be much in the way of crossover. If one lot - gets sick of me, there's always the other bunch."

So which does he prefer, the science fiction or the straight stuff?

"I probably prefer doing the science fiction, there's far more freedom in it. With the mainstream stuff, there are fixed things that you can't change, parameters that you're not allowed step outside. But when I'm doing sci fi, I get to use up all my what if fantasies, all the torpid, vaguely sexual stuff that floats around in my brain."

Banks's science fiction, which includes landmark works like Consider Phlebes and the demonically funny Feersum Endjin, initially met with scepticism from the anorak establishment. But this captious audience eventually became captive, once the true depth of his storytelling was appreciated. Unlike those who merely conjure up B movie monsters, he looks backwards as well as forwards, ladling thirstily from a murky, primordial soup.

"The thing you must remember about science fiction is that people are reading it to escape. There's this notion doing the rounds that fantasy is increasingly popular because of some form of pre millennial angst. Tosh. People just want to imagine that their lives will be better or more exciting in the future, or might have been in the past. You know, they want to think of times when men were men and swords were sharp. It puzzles me, in a way, that my science fiction is enjoyed cos my visions tend to be dystopian rather than utopian.

Banks's own lifestyle certainly smacks of a sort of Highlands utopia. Settled with his wife near his native Fife, he passes his days belting hell for leather around the heather on a collection of motorbikes and fast cars. He works three or four months of the year.

"The ritual goes something like this. If it's going to be a long book, I start in October; a short one, I start in November. The first draft is done by Christmas and then I take a couple of weeks off. Unless the writing has gone particularly badly, there's just a week or two of revisions to be done in January. That's it, the book comes out in August."

Sounds remarkably quick ... "Oh aye, it's the blitzkrieg approach. Basically I'm a slacker so I cram all my work into as short a space of time as possible. I did try this business where you're supposed to sit down and write a bit every single day. (Collapses in hysterics.) Oh dear, oh dear! That just wasn't me at all."

Does he fit the usual writer's psychological profile? Is he a depressive insomniac with an enormous ego?

"Depressive, no. Insomniac, no. Enormous ego, absolutely! It probably comes from sitting around inventing little worlds, playing God. I think there are as many types of writer as there are types of people but yes, large egos might well be a common thread."

Banks's reputation was given another boost recently with BBC 2's acclaimed serialisation of The Crow Road. Was it a bit of a cringe, seeing the characters "brought to life"?

"Not at all, I thought they did an absolutely superb job. To be perfectly honest, I had very little involvement with it, bar providing the initial storyline. That's probably why it turned out so well."

Flitting happily between straight and science fiction, is he ever tempted to try out other genres? "Oh very much so, yes. I'm frequently tempted to go off and molest some other genre, maybe a horse opera! Or perhaps I could dig out another initial: write some pornography and call myself Iain X. Banks!"

It's certainly a thought. Apart from four impoverished, "studently" years in darkest Hackney ("a very drab place") and four more in exotic Faversham ("almost unnaturally dull"), Banks has spent all his life in Scotland. Oddly, he's rarely name checked when talk turns to the new Scottish school of fiction.

"I think that's because my work tends towards the generic and also, of course, there's the fact that I'm not quite what you'd call a young writer anymore. But I'm thrilled silly that so many Scottish authors are getting recognition now. Scottish writing is definitely punching above its weight."

Banks's next novel, a mainstream one, is provisionally titled A Song of Stone, and will be published in August.

"It's a return to grim. The books have been almost wildly happy for the last while so it's time to move away from that." The "grim" of which he speaks is a type of sepia-toned melancholia that has coloured his straight novels. Combined with a very dark humour, it has distinguished works like the best selling Whit and the eerie Complicity. He's also a past master at cutting straight to the action. The first line of The Crow Road: "It was the day my grandmother exploded." This talent for spinning a ripping good yarn has had him described as "1990s Robert Louis Stevenson".

"I sincerely doubt if I'll every turn out anything as everlasting as a Treasure Island. I think that's just hyperbole really, though it would be nice if it were true."

Who's to say he isn't? The Wasp Factory recently came in at No 31 in the Waterstone's Top 100 Books of the Century poll, just behind Nabokov, just ahead of Proust.

Banks is in Dublin next weekend to attend the Trincon 2 Sci Fi seminar at (or should that read) TCD? (See panel.) He is a veteran of such gatherings.

"I used to end up at four or five a year, so I've had to cut it down a little. You just worry about saying the same things over and over."

Is he usually mobbed by gurglingly obsessive Iain M. Banks fans? "That's what I used to hope would happen. But as it turns out, Iain M. Banks fans are very pleasant, very normal people. Far more normal than me, in fact."

He visits Ireland, briefly, around once a year. "This time, we're going to do it properly. My wife wants to see the Giant's Causeway and all these places so we're going to tour around. We'll probably end up stood there in the rain saying daft things like: `Oh, isn't it pretty. It's a wee bit like Scotland, only different'. I'll enjoy myself thoroughly but whether I'll remember anything afterwards is another matter entirely."