Iain Banks: I never had any illusions about Gordon

Iain Banks has a new passport. That's nice, you might think – poor fellow for losing the first one. But he didn't. He ripped it up and posted it to No 10, in anger at the invasion of Iraq. "I said I wouldn't get a replacement," says the novelist, "until the man who took us into that disgraceful, illegal war had gone."

He has now. And you've got to keep in with the neighbours, haven't you? Banks lives in the Fife town of North Queensferry, where he grew up, and his home is a very short walk from that of Gordon Brown. Just a few days after the man up the street took over from Tony Blair, Banks found himself filling in a replacement request form, and having to explain what had happened to the old passport: "Sent to PM in protest".

The original gesture was slightly less futile for Banks than it might have been for the rest of us, because of his profile as one of the most popular authors in the country and the fifth greatest British writer of all time, if we believe one infamous internet poll (surely skewed by net-head fans of his science fiction, a thought that makes him – literally, oddly – say: "Tee-hee!").

Next week, his most recent mainstream novel, The Steep Approach to Garbadale, is likely to be named as the winner of the first Clare Maclean Prize, which sets out to identify the best work of fiction by a writer born or based in Scotland. It will be presented at the end of Aye Write! – a major festival featuring the Hollywood star Kathleen Turner and writers including Hanif Kureishi, Louis de Bernières, Joanne Harris and Banks.

Having come down by train to visit bookshops, he is presently sitting in the office of his publisher, Little, Brown, in the imposing Unilever Building by the Thames. Banks is usually described as looking like a polytechnic lecturer from the Seventies, but he has changed lately. The black specs are fashionable. The silver hair is feather-cut a little more tidily, the beard trimmed more closely. He is wearing a brown leather box jacket of exquisite softness – "Feel that!" – which he reveals, reluctantly, to be Nicole Farhi. What's going on? Why is this renowned lover of gadgets, guitars and computer games suddenly in posh clobber? And – thinking about it again – why did someone who has often declared himself a proper socialist forgive Gordon Brown so easily for his part in the war?

"It was Blair's war," insists Banks. "He lied to the Cabinet, lied to the Labour Party, misled Parliament, lied to the British people. And I never had any illusions about Gordon, so I'm not disillusioned."

The passport came back quickly. "I had thought there would be more fuss." He sounds disappointed, but not much can take the bounce out of this 54-year-old who has a sunny disposition as strong as his imagination is grotesque.

People do unspeakable things to each other or die horribly in his novels – sci-fi or not – but through them all runs a dry wit and jauntiness. Actually, all his main characters are a bit like him.

"I know. It's a failing. I recognise that." Which is disarming, just as he is if you call him smug. "Yes. Can't help it. Sorry." And why wouldn't he be? After 10 years as a dustman, hospital porter and clerk among other jobs, just to pay for his writing, Banks was published in 1984 and had a huge hit with his debut. The Wasp Factory, whose young protagonist tortures insects and commits murder, is still his most famous book. The Crow Road, filmed by the BBC, probably comes second. There have been 17 others, including the sci-fi that sells in stacks.

The latest is Matter, a thumping great book with appendices, full of jargon and in-jokes about The Culture, a society of his own creation which is as labyrinthine as anything invented by Tolkien. It is a land of plenty, where poverty and ill-health have been abolished and almost everyone is happy – except for the agents of the Special Circumstances Section who do anything necessary to maintain the greater good. Sounds like the way the authorities justify detention without trial, doesn't it?

"Absolutely not," he says quickly. "The Culture is my idea of utopia. It's pure wish fulfilment. This society is driven by the urge to do good – not, like capitalism, by the urge to exploit. We are turning into a police state in this country. The police are able to get away with anything, including killing innocent people."

The rant that follows is delivered with bar-room relish and a little jiggle about on the sofa, but he means it. "Security people are largely, in effect, complicit with the terrorist who wants to make our lives hell," he says. "The security people say, 'Right, we'll help you with that. We'll make people take their shoes off and not be able to go through unless they're carrying little delicate bits of plastic with their fluids inside. You know, what the fuck are you talking about? It's nonsense. It's arse-covering. It's extreme overreaction. It's not making anyone safer at all."

There is a way to do that, he says. "Stop invading. Life is actually quite simple: don't start fights." This from the man who says that he has "always loved explosions and conflict and big things getting clobbered by bigger things". But that's fiction. He well knows that he is not really Sun Earther Iain El-Bonko Banks of North Queensferry (his name in The Culture style).

Nor is he really Iain M Banks, by the way, as it says on the cover of Matter. Menzies was supposed to be his middle name, but his father got it wrong on the birth certificate. Still, it is a useful way of telling his sci-fi from his twisted tales about ordinary, everyday sadists and murderers, which are published under the shorter Iain Banks.

Banks has a home close to the Forth Bridge, his favourite building, in the town where he lived until he was nine. Then his father, who worked with the Admiralty, was moved over to the west coast. Educated at Greenock High School, Banks describes himself as "a sufferer" for supporting Greenock Morton FC. "Not much fantasy there, I'm afraid."

He still goes: that's the point. He still has friends from school and Stirling University, and goes for curries with them all the time. He lived down south for a while, but has been back since 1988. Lately, he has taken to voting for the Scottish National Party. "I think there is still a chance to save a more communitarian, socialist ethos within Scotland," he says. "I'm all in favour of abandoning England to its monetarist, privatising hell."

As a child, he shocked his parents by declaring himself more British than Scottish. "It was a lot to do with things like the BBC, the GPO and the NHS. Institutions with three letters. So much of that stuff has been or is being privatised. That has kind of destroyed what Britain meant to me."

An independent Scotland would do well in Europe, he insists. "We had 300 years of being ruled from a foreign capital with a different currency. We're used to all that. We don't have England's post-imperial self-importance."

Some people say Europe might not want Scotland, he says. "Can I point to a 200-mile fishing limit around the Scottish coast, full of fish? I think they'll want us with open arms. Not to mention the whisky."

Ah, the whisky. His 2003 travelogue Raw Spirit was essentially a tour of distilleries. It was also a diversion from his regular routine, which involves taking half the year off, then spending three months wandering about the hills dreaming up a story. "I have always been comfortable in my own company," he says.

Then he writes for three months. Eight hours a day, five days a week, somehow producing 3,000 words a day. "I am due to start on the middle Monday in October. It's windy and dreicht then; you might as well sit in and write a book."

From this, he earns £250,000 a year. In addition, he appears to have emerged from a mid-life crisis a healthier, happier, more responsible citizen. The swine. He is divorcing Annie, his wife of 25 years, – "it is as amicable as these things can ever be" – and living with a new partner/girlfriend (he uses both words), the horror festival founder Adele Hartley. Look no further for the cause of the new wardrobe.

Instead of buying a fast car, he has sold an entire collection. "I thought I'd save the world personally," he jokes, "so nobody else has to bother. I got rid of the two Porsches and the very fast BMW and the behemoth of a Land Rover. And the motorbike."

After falling off. "Yes, well, that was the real reason I got rid of that one."

So what brought all this on? "Nothing in particular. Thirty years of reading the New Scientist. I want to be able to look my many nieces and nephews in the eye and say that when I realised there was a proper problem I tried to do something about it." He won't fly unless it's an emergency either. "We christened my new passport by going to Venice on the train." He says that as if we all have a choice between easyJet and first class on the Orient Express.

Smug? Definitely. But likeable. Trying to wear fame and fortune like he wears that Nicole Farhi jacket: aware that it's absurd, but loving the feel of it anyway. "I'm lucky," he says, smoothing the sleeve. "And I can't spend it all on cars any more, can I?"