IT IS some time in the future. Scotland has unilaterally declared independence from the rest of the UK. A journalist who lives on Bute is crossing the border into England, but it isn’t easy. There are extra security checks: retinal scans and residency permits. He also finds, once he gets there, that the England he knew has changed: many of the shops are boarded up, some of the houses have high security fences, and the authorities are prowling around London looking for illegal immigrants. “I had the uneasy sensation that I no longer spoke the language,” says the journalist, “as if I was abroad.”

In some ways, this is classic Christopher Priest. Britain’s pre-eminent writer of literary science-fiction is an expert at taking the present and giving it a dark future twist, but there’s also something more to it this time, something more personal. The journalist who crosses the border from a future Scotland to a future England is Ben Matson, the central character in Priest’s new novel An American Story. However, at least some of Ben’s story comes from what’s happening now, from the dark and twisted present, from Priest’s own experiences.

He tells me about a taxi trip he took a while ago in Devon, where he used to live. “We were in Devon which is rural and peaceful and all of that,” he says, “But I was in a taxi being driven by a Lithuanian guy and I asked him ‘do you ever get harassed?’ and he said ‘every day’ and I said, ‘what? in Devon?’ People also had UKIP flags and I thought I don’t like this. Something horrible is going on, and after Brexit I said it’s time, let’s move. I don’t want to be in England anymore.”

And so Christopher Priest and his partner Nina Allan, also a writer of science fiction, got in their car and drove up to Scotland looking for somewhere to live, stopping at Dumfries and Kirkcudbright and Kelso before settling on Bute. They now live in a house that was once a doctor’s surgery and remnants of those days remain: above the door to what is now Priest’s library and office is a sign in big letters that says: “waiting room”. I suggest jokingly that maybe he could set up here as a consulting novelist and give advice to young writers. “I’d advise them not to start,” he says.

He’s joking really. Priest, who’s 75, has had a long and successful career as the creator of great science-fiction novels including his most famous The Prestige – it’s just that his career as a novelist has been a little on his mind of late, because the day we meet, August 28th, marks the 50th anniversary, to the day, of him becoming a full-time writer. Until August 28th, 1968, he was working in accountancy, but he gave it up to write fiction. What made him do it, I ask. “Two words: you’re fired.”

At first, it was difficult – he only had about 50 quid in the bank – but by the early 1970s, Priest had emerged as one of the most exciting practitioners of the British novel of ideas. It was probably, looking back, a bit of a heyday for science-fiction, although Priest says it didn’t feel like it at the time. He also says the problem now is there’s just too much science-fiction and most of it is terrible or trivial – none of which helps what he sees as the constant problem of readers, literary editors, or critics, dismissing science fiction. “People have a s*** detector,” he says. “Ooh, that smells of science fiction.”

Obviously, Priest is operating at the other end of the scale with serious novels that often explore how illusions can feel like reality, and An American Story is a fine example. The premise is that the journalist, Ben, is still trying to deal with the fact he lost his girlfriend in the 9/11 terrorist attacks, or at least he thinks he did, as her body was never found. Twenty years on from the attacks, an unidentified plane is recovered from the sea and it is apparently the same plane that crashed into the Pentagon – the plane that Ben’s girlfriend was on. So how is that possible? What happened? Did the plane crash into the Pentagon? Did his girlfriend really die?

Sitting in his office talking about the novel, surrounded by some of the books on 9/11 he used for research, Priest is aware that he is sailing into difficult territory here. Was he cautious about tackling 9/11 in case people saw him as one of those conspiracy nuts who spread their theories on social media? “I don’t do social media for that reason,” he says. “What we’ve done with social media is we’ve given everyone an equal right to be heard and most of those voices aren’t worth hearing. Facts have been replaced by wacky opinions.”

An American Story is different: it’s a platform for exploring serious ideas about 9/11 and the way we experienced it and remember it, some of which touch on Priest’s favourite themes: how our perception of a situation can be wrong, how memory can be false, or how we can build a whole pyramid of facts based on our prejudices. All of this applies to 9/11 big-time, believes Priest.

The ideas around the plane that was crashed into the Pentagon, after terrorists stormed the cockpit, are particularly interesting. “The weirdest thing for me,” says Priest, “was the flight data recorder of the plane – this is in the book. It follows what the flight did and the data comes on a spreadsheet. It’s got about 4000 columns and each deals with a certain part of the aircraft - every door has a column, every passenger seat. And one of the most interesting things was the cockpit door has a column and the door never got opened during the flight.”

Priest doesn’t believe that this and other apparent inconsistencies mean there was some massive conspiracy to stage an attack and blame it on terrorists – rather, he thinks there were some mistakes made in the authorities’ response (particularly in getting jets into the air in time to intercept the hijacked planes) which were then covered up. “All of a sudden it becomes this thing where they can’t admit what they’ve done and it gets bigger and bigger,” he says. “It was a f***-up”.

The beauty of An American Story is the elegant and unsettling way in which Priest explores these ideas, and the consequences of false memories and false beliefs. He has done the same in many of his other novels and no doubt will do so again in his next one, which is set in Paris. Priest tells me he’s just about to leave for the city for a five-week research and writing trip, but he’s already looking forward to returning to the life he’s made for himself here on Bute. Has it lived up to his expectations?

“I’m hoping Scotland is better,” he says. “There are differences - they’re licensing fracking all over the place in England and there’s a moratorium here. There’s active encouragement of the arts. There’s also little touches that we like, like the NHS – much better here. I’m not saying it’s perfect – there are problems – but it’s not the same problems as there are in England.”

Priest’s new life in Scotland has even made him question his opposition to Scottish independence. “When I lived in England and the Scottish independence debate happened, I fervently wanted it to fail,” he says. “I see Scotland as an integral part of Britain for all sorts of reasons, some sentimental, some practical. Now I live here, I’m not so sure.”

However, there is at least one problem he can foresee with independence, foreshadowed in all those border checks in An American Story. “Talk about the land border problems they have in Northern Ireland,” he says. “That would be nothing to Hadrian’s Wall!”

An American Story by Christopher Priest is published by Gollancz at £20.