Shortly after I joke that Sir Ian Rankin’s social media gives the impression visitors to Edinburgh are pretty much guaranteed to bump into him, a US tourist shuffles over to tell the author his bestselling Inspector Rebus novels are among his reasons for coming to the city.

In fairness, we are sitting in The Oxford Bar – Rebus’s preferred watering hole and practically a clubhouse for his creator. Photographs of the author adorn the walls and, as we enter, the landlady hands over a stack of correspondence, some addressed simply: “Ian Rankin,The Ox, Edinburgh”.

But there is a ubiquity about the 62-year-old, especially, I say, if you follow his daily peregrinations around the city on Twitter.

He smiles: “Well, I walk everywhere, I don’t get taxis or buses. There’s always meaning though, I’m going to meet someone or do an interview. I’m not the sort of writer who’s made their money and started buying designer clothes and a fast car.”

It’s reassuring that despite 30 million book sales and counting, Ian hasn’t been forced to abandon the Edinburgh he’s brought to life and championed in his stories.And the Ox is the ideal place to have a drink, soak up the atmosphere and chew over his stellar 36-year career as he publishes his 25th Rebus book, the brilliantly titled A Heart Full Of Headstones, of which more shortly.

Settling down with a pint, he admits the plot of 1987’s Knots And Crosses – which introduced his soldier turned cop, still carrying the mental baggage of his time in special forces – came almost fully formed.

“I’ve still got the notes. It’s a lined sheet of paper that says, ‘Guy is being sent matchstick crosses and knotted pieces of string and he doesn’t know why’,” he recalls.

“I’d signed the contract for my first book, The Flood, my literary novel, that day. I came back to my digs, sat down and John Rebus jumped into my head. It’s like he was waiting for me.”

Growing up in a tough Fife mining community, Ian had no pretensions about writing. “As a working-class kid, I wanted to write books people would pay to read,” he admits. “I was a big fan of Clive Barker and Ramsey Campbell and I thought, ‘Oh, these books sell a lot, maybe I should write horror?’ I did start pencilling one out but it never got anywhere. I wanted to sell enough copies to be a full-time writer, but be respected within the literary community.”

An ambition achieved, I suggest.

“It took a long time, and it’s a double-edged sword writing a series,” he smiles. “I think it does put folk off, too, looking at my books and there are 24/25 in a series, they might think, ‘I don’t want to start that, it’s a big commitment’.”

Knots And Crosses’ intriguing protagonist and twisting plot set the template for later books, but life went on unchanged and Ian’s next efforts were spy novel Watchman – “an attempt to become John le Carré” – and techno-thriller Westwind. Neither sold well.

Then his editor asked: “Whatever happened to that guy Rebus, I liked him?”

Ian continues: “And I went, ‘Yeah, I liked him too, maybe I should give the crime novel another go?’ Nothing else I’d tried had worked. Once I’d done two or three, I was set in my ways, but there was a time when it might not have been so.”

Hide And Seek, Tooth And Nail, and Strip Jack followed in swift succession, but success remained elusive. It wasn’t until the eighth Rebus book Black And Blue won the coveted Gold Dagger for best crime novel of the year that things started to change. “The book after that, The Hanging Garden, spent one week at number ten in the bestseller lists. It was Rebus book 11, Set In Darkness, before I hit number one.”

Were he starting out today, Ian doesn’t believe he would have a chance.

“The bean counters now say you make it big and young or you don’t make it at all. I’m very happy I grew slowly,” he says.

“By the time success came, I was levelheaded. If Knots And Crosses had been a worldwide hit, I’d have been completely insufferable; it’d have been helicopters everywhere and gold-plated pinball machines in every room of my mansion.”

“Today Ian and his wife Miranda, a civil servant turned professional tapestry weaver, live modestly, giving 30-40 per cent of their net annual income – a decent six-figure sum – to charity. The couple have two children, including younger son Kit, 27, who has the rare genetic condition Angelman syndrome and lives in care near the family home.

Ian has spoken movingly of how his anger at Kit’s condition informed his early work when the family was living in France and he was struggling to write. The passion – and anger – remain. A Heart Full of Headstones opens with Rebus – now retired and facing ill health and loneliness – in court on a murder charge and ends on a brilliant cliffhanger.

It was written in an intense burst of creativity with its deadline fast approaching.

“I couldn’t quite make it work. In January we went on holiday to St Lucia and I had a June deadline for a book I hadn’t even started,” he explains. “It just started to come. I would tap in notes on my iPhone of what I thought this book would be: who was in it, what was happening, why it was happening. I came back to Edinburgh, typed up the notes and started writing. It almost wrote itself.”

The book, which centres on a corrupt west Edinburgh police station and domestic abuse claims against an officer, was inspired by recent scandals.

“There’s a general feeling in the crime fiction world: ‘Are detectives and police officers the knights in shining armour they’ve always been portrayed as?’ That’s a problem I think a lot of writers have. Are we doing PR for the police or just providing a comfort blanket for readers? We should be confronting them with hard truths, not just giving them easy answers, and when you look at the real world, you see all kinds of malfeasance happening.”

The book was inspired in part by two cases: the murder of Sarah Everard by a police officer and the killing of sisters Nicole Smallman and Bibaa Henry, which sparked outrage after it emerged cops at the crime scene had taken and shared photos of the victims.

came to my down jumped head. he was for “I was looking at aspects of English policing and moving them to Scotland to discuss them. I was thinking, ‘Are the police still the good guys? Why are these kinds of people working for them and why do they think they can get away with it?'” Critics are already raving about the book. But how does he keep them fresh after so long?

“I decided early on that Rebus would live in real-time, so when I sit down to write a book, his life has changed,” Ian explains.

“Starting out, he’s a young macho, brash cop, then he’s a bit seasoned and cynical, then he’s retired; now he’s got health issues, he’s divorced, never sees his daughter. So whenever I write, it’s like dealing with a new character. That keeps me on my toes.”

Rebus, played on screen by Ken Stott and John Hannah, with a potential new TV adaptation in the works, was 40-ish when readers first met him (his author was 27) so his ageing was always an issue.

Ian smiles: “Obviously, I didn’t know I was going to be writing about him for so long. But enough time had to have passed for him to have blocked off his Army experiences.”

Ironically, when writing that first, fateful crime novel, at one point he even considered killing Rebus off. He shakes his head now at how that would have changed the course of his career and life.

At this summer’s Theakston Old Peculier Crime Writing Festival in Harrogate, US crime-writing titan Michael Connelly, one of the few writers globally who can rival Ian’s popularity, spoke about the ageing process of his own iconic detective, Harry Bosch.

Asked if his character, who is now 72, might die, Connelly admitted: “If my goal is to show a complete life, I think I should show that. At some point I could, for lack of better words, kill Harry Bosch off… I would like to write the end of the story.”

Ian nods in agreement: “Bosch and Rebus have had very similar trajectories. They’re both ex-Army – Bosch served in Vietnam, Rebus in Northern Ireland; both have broken marriages; both have been cops then retired, come back in, and been private detectives.

“I’d be interested to know what Michael has got in store. For Rebus, I just don’t know. But the clock is ticking – for me as much as for him. Whenever I sit down to write, I hope I’ve got one more book in me. Is it a Rebus book? Who knows?”

Fans will have to wait to find out. “I’m taking next year off or I’m getting divorced,” Ian laughs. “My wife says we’re going on a year-long holiday or she’s walking away, so there’ll be no writing, no festivals, no appearances… just fun while we still have our own knees and our wits about us.”

There may, however, be a new Rebus stage play, written in a burst of lockdown creativity. Ian is well known for his collaborations, including with the cult Scottish songwriter Jackie Leven – whose lyrics have inspired three book titles, including the current hardback – The Charlatans’ singer Tim Burgess, and Anthony Bourdain, the late chef-turned-writer and broadcaster.

“I interviewed him on stage, and he had this attaché case with him. I asked what’s in it and he had brought his chef’s knives from New York because he didn’t trust anyone not to use them,” says Ian.

“I took him to The Oxford Bar and he loved it and wrote about it in one of his travel books, ‘I’ve been to the best pub in the world but I’m not going to tell you where it is or you’ll go there and spoil it!'” Despite his keen twitterings, Ian has largely avoided the so-called culture wars.

“I’m much happier staying out of the whole thing,” he says. “I write fiction. The real world is not part of my gamut.”

As for his ennoblement – he was recognised in the June birthday honours for services to literature, and is disappointed he won’t now be knighted by the Queen – he admits: “It’s a double-edged sword in a country that has a large republican community.

“My parents aren’t around but they’d have been chuffed, and I looked at the list of Scottish working-class writers who’ve been knighted and, basically, I’m it. I just thought ‘Well, a working-class guy from a mining community in Fife, why not?’ I phoned my sister and said ‘I’ve been knighted,’ and she said, ‘Ah, but you’re still my wee brother’. It keeps you grounded.”

• A Heart Full Of Headstones by Ian Rankin (Orion, £22) is out now. To order for £18.90 with free UK P&P, visit expressbookshop.com or call 020 3176 3832