IAIN BANKS WAS ONCE ASKED what his motto was. The answer? “Oh, what the hell.”

A bit flippant for a life philosophy, perhaps, but it’s an attitude that has made for a brilliant, breakneck career: having set heads spinning with his gruesome, gothic debut The Wasp Factory in 1984, Banks has published a further 22 books in the subsequent 23 years, a production rate not matched by any of his peers from the Granta Best of Young British Novelists list of 1993.

Alternating between “main-stream” fiction (epitomised by his No 1 bestseller The Crow Road) and high-concept sci-fi (written under the name Iain M. Banks), he bashes his books out in about three months apiece. The rest of the time he likes to spend strapped into speeding machines or laying into politicians. (He was so outraged at the Iraq War that he cut up his passport and posted it to Tony Blair.)

So it seems a particularly Bank-sian moment when, towards the end of his new novel, The Steep Approach to Garbadale, the protagonist, Alban, returns from a long hill-walk and is faced with a choice of paths down to his house: a slow, sensible, zigzag route, or “a frantic bit of scree-running” – a direct scramble over a mass of broken stones. It is obvious which he should take – not only is scree-running dangerous, Alban thinks, but it also damages the landscape. He pauses for a moment, and then, with a whoop, pitches himself on to the slope.

Even here, smartly dressed and sipping mineral water in the restaurant of a fancy London hotel, there is an edge of wildness about the 53-year-old Banks – in the irrepressibly curly hair and glinting eyes, the impatient eyebrows and thunderous laugh. Surely, I ask, Alban’s wild run is an expression of his own devil-may-care philosophy? Actually, no. It’s just an excuse for a catchy title: “One day ‘The Steep Approach to Garbadale’ came into my head, and I thought, I like that, but there’s no bit in the book to justify it . . . oh, better write one,” he says, rocking forward with laughter.

“I’m not a particularly analytical writer,” he explains later. “If it works, it works . . . It’s almost a superstition: if you look into it too much you might destroy the magic.”

Happily, it does work, and The Steep Approach to Garbadale, with its sharp-tongued protagonist, feuding family and dark secrets, is full of Banks’s familiar magic. In it the Wopuld family, creators of the bestselling boardgame Empire!, are on the brink of selling their business to the slick American Spraint Corp – for a hell of a lot of money.

They have all been invited to Garbadale House – the Wopulds’ monstrous castle in the Highlands – to decide the company’s fate, under the controlling eye of Grandma Win. Alban, the black-sheep boy, is persuaded to return from his self-imposed exile and join his cousin Fielding in an attempt to convince the rest of the family not to sell. But Alban has his own issues – a forbidden childhood love affair with a cousin, a complicated relationship with a mountain-climbing maths professor and some unsettling information about his mother’s suicide.

It’s tremendous fun, but Banks has already written the ultimate family saga, The Crow Road. Why revisit old territory? “Families are just such fertile ground,” he says. “We’ve all got one, and they’re all a bit mad.” Like Alban, Banks is an only child with lots of cousins (at one stage he counted 30). Growing up in North Queensferry in Fife (where he now lives again, next door to his parents), he had the best of both worlds: “I was thoroughly spoilt and loved by my parents, and I had the camaraderie of an extended family.” They loved weddings, christenings, and “any excuse for a hee-ha”.

At home, Banks was developing an interior life that prefigured his later career: “I couldn’t get to sleep at night. My wee brain was buzzing away for hours, and I was too young to masturbate, so I made up stories in which I was the hero – a young James Bond.” When he discovered that there were things called writers, he knew he wanted to be one. “I was 11 years old, and we were asked to draw what we wanted to be when we grew up. Everyone was drawing space-men and firemen, and I drew a writer – except I couldn’t envisage what a writer looked like so I drew an actor onstage and in the top left-hand corner wrote ‘and writer’ in big white crayon letters.”

At the same time he was developing a passion for games. His father, who was a first officer (second in command of a ship) in the Admiralty, brought back old nautical charts, and on the reverse young Iain devised the sprawling, territorial Super Risk – a game so complicated that he could never teach it to anybody else. It’s an enthusiasm that hasn’t faded: he recently became so addicted to the computer strategy game Civilization that he had to throw out the CD. Games, Banks points out, share a lot with stories: “I love the linearity – they’re not like paintings, which you take in all at once. You start off with a theme, which is then modulated by other ideas. In the end it’s always a metaphor for life.”

Initially, Garbadale was going to dramatise that metaphor in a much more “weird and wonderful” way, with its characters actually trapped inside a game (like the film Jumanji, he says, and I am momentarily stunned at this edgy novelist taking his lead from a mid-Nineties Robin Williams kids’ flick). But Banks quickly realised that this wasn’t going to work, and settled for the boardgame as a symbolic device, framing the Wopulds’ struggles and divisions. In one witty passage, the changing editions of Empire! are used to tell the history of the 20th century, from the remapped Commonwealth (“no exclamation mark”) after the Second World War to the disastrous hippy spin-off Karma!in the Seventies.

“The sort of novels that I like to write are driven by ideas and not characters,” Banks admits – which explains why he feels so comfortable writing science-fiction. It also explains why his favourite of his literary novels is The Bridge: an exhilarating collage of dreams taking place in the head of a coma victim. He’d love to attempt something like it again. “Something with lots more techniques and voices” – like David Mitchell’s Cloud Atlas, which was so good that it made him feel “slightly jealous, and that doesn’t happen often”. But he knows it’s going to be hard. “As you get older, you have fewer ideas, although you’re better at using them.”

So far, ideas have never been a problem for Banks – it’s self-restraint that he lacks, particularly when it comes to politics. His last novel, Dead Air, about a left-wing shock-jock, was suffocated by sustained rants against fundamentalists, Holocaust-deniers and Eurosceptics. In Garbadale the estate manager gives a lecture on the reality of global warming, and Alban mounts his soap-box for a vicious attack on American imperialism. Does Banks worry about putting words into his characters’ mouths? He looks sheepish: “It’s a privilege to have the platform and you have to be careful not to abuse it, but on the other hand having opinions is part of what being a writer is about. I’m not claiming I get the balance right every time.”

It’s no secret that the opinions in Garbadale are Banks’s own. Ask him about the Iraq War, and he launches into a bitter soliloquy even more convincing than Alban’s. Ask him about the environment and you’ll find that he practises as he preaches: a self-con-fessed “petrol-head”, he has whittled his four cars down to one – a Lexus Hybrid – in an effort to reduce his “carbon hoof-print”, and is downgrading his beloved Honda motorbike. He gave up learning to fly a couple of years ago, although that was just as much because he was splitting up with his wife and couldn’t concentrate.

He’s toned down his substance abuse too: having consumed 80 bottles of whisky “researching” his book about the drink, Raw Spirit, he’s barely touched the stuff in the four years since; and having tried “pretty much every drug I could find” apart from heroin, he can no longer be bothered with them.

Banks’s appetite for music, however, is undiminished: he shares with a character in Garbadale a deep-rooted love of Led Zeppelin (the first three albums he bought were Led Zeppelin, Led Zeppelin II and Deep Purple in Rock), but is hip enough to name-check the new indie band Arcade Fire too. He plays “guitar, badly” and “keyboard, badly” and can quite happily hole himself away for hours, recording “complicated rock songs” and classical piano pieces. His ambition is eventually to work up to a symphony.

And why not? Striding into his second half-century, Banks is determined not to let himself be intimidated. “As you get older, you draw into yourself and think ‘I can’t do that’, and as soon as you start thinking like that, you can’t. You have to have a wee bit of a nutter mentality – at some point you have to think ‘Oh, what the hell’, and go for it.” Spoken like a true scree-runner.

The Steep Approach to Garbadale by Iain Banks

Little, Brown, £17.99 Buy the book from Books First £7.59 including free delivery

The essential Iain Banks

The Wasp Factory

Frank is going through one of those teenage phases. You know the sort of thing: sticking mice heads on poles, murdering cousins, constructing complex prophetic rituals based on insect torture . . . In 1984 The Times judged The Wasp Factory “crassly explicit”, obscene and, in conclusion, “rubbish”. We were very wrong. It is in fact the perfect first novel: witty, shocking and wildly original.

The Crow Road

“It was the day my grandmother exploded.” So begins a blackly comic rollercoaster of a book, narrated by one Prentice McHoan; a smart, charismatic adolescent whose discoveries of sex, drugs and religion are being overshadowed by his eccentric family’s exploits – particularly his uncle’s mysterious disappearance. Dramatised with flair by the BBC, this is Banks at his most bankable.

The Bridge

Banks’s personal favourite. A car crash victim lies unconscious in hospital, while in his mind he explores an Orwellian city enclosed in a giant bridge. As he tries to recover his lost memories, fragments of his past flash in front of us. Dreams breed visions and ideas burst from the seams in an inspired novel that skirts the boundary between Banks with and without his sci-fi “M”.

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