William Boyd stays away from the Zeitgeist. He’s not interested in writing about current events. “In two or three years’ time, nobody will care and nobody will know what you’re talking about. It’s just looking for obsolescence.” Nor does he care for the literary fashion for sticking closely to your own experiences. “Your life has to be pretty damn interesting if you’re going to foist it on the reading public. Why not make it up?”

Making it up has worked rather well for Boyd, 70. He’s spent the past half century tossing out big, rich novels set mostly in the recent past. There are the century-spanning “biographies” that follow single characters through their whole lives: The New Confessions (1987), Sweet Caress (2015) and, of course, the 2002 Booker longlisted Any Human Heart. There are the African novels (his 1981 debut A Good Man in Africa, later a film starring Sean Connery; An Ice-Cream War, which was Booker shortlisted in 1982), the spy thrillers (Restless won the 2006 Costa prize), the screenplays and the short stories.

The evidence of his relentless output fills his exquisitely bohemian terraced house on a quiet street in Chelsea, West London (although it wasn’t so quiet in the Nineties, he reminisces, when his then-neighbor Paula Yates left Bob Geldof). The living room table is piled high with books — Iris Murdoch’s The Bell catches my eye — and downstairs I glimpse a shelf of Boyd novels. Well, fair enough — this latest is his 17th.

The Romantic plops the reader down at the dawn of the 19th century. It’s another of what Boyd calls “cradle to grave” narratives — we follow the hero, Cashel Greville Ross (Boyd likes splashy names), as he roams across the century. The pages brim with famous names and exotic locations — with Florentine palazzos, New England farms, Byron and the Battle of Waterloo.

The 19th century may feel remote to most of us, but Boyd, who spent eight years teaching the Romantics paper at Oxford and half-writing a PhD on Shelley, had an “an unused mass of material” ready and waiting. “I was steeped in that early 19th-century world. Nothing is wasted.”

“In two or three years’ time, nobody will care and nobody will know what you’re talking about. It’s just looking for obsolescence.”

Then he happened to read The Life of Henry Brulard, a fake autobiography (“my territory”) by the great 19th-century writer Stendhal, neglected by English readers today, but still revered in France (“he’s up there with Flaubert or Balzac”).

Boyd was struck by Stendhal’s outlook. “He thought of himself as a Romantic, but he saw it as a kind of disease. He was a funny, ugly little short man who kept falling in love with beautiful women. He regarded his romantic nature as a kind of torment.” Cashel Greville Ross was born.

The more famous Romantic poets are also leading characters in the novel. “I’ve always been keen on demythologizing Shelley and Byron. If you say Byronic or Shelleyian, you probably get completely the wrong impression of the two men. I remember when I was doing my thesis I was struck by Byron’s mistress writing that Shelley had very bad skin.”

As for Byron, “he seems to have been a singularly horrible human being, although of course massively talented. The life he led was really Jeffrey Epsteinesque” (he had a penchant for teenage mistresses). “I thought, ‘Let’s see if I can paint a realistic portrait of those times and plonk my fictional character down among them and shine a harsher light on these mythological figures.’” Boyd is quick to point out that he’s writing fiction, not history or literary criticism. “You have this license and I don’t hesitate to exploit it.”

Boyd spends longer researching than writing. He likes to accumulate “a small library” of cheap second-hand paperbacks for each novel he writes, much to the despair of his wife, Susan.

“How long did it take to get a letter from India to London in 1822? I don’t know, but I’m sure I can find out. One of the advantages of spending many years not finishing a doctorate is you do know how to look things up.”

Lord Byron “seems to have been a singularly horrible human being, although of course massively talented. The life he led was really Jeffrey Epsteinesque.”

In the end he discards “95 per cent of the research” because “you can’t just pack the book with information. You’re looking for that nugget in the ore.” He mentions a scene in The Romantic in which Cashel wakes up from a bad dream in the middle of the night and instead of flicking on a bedside light as we would, has to spend a couple of minutes messing about with flint and candles. Such details bring the book to life.

He is fascinated by the technological upheaval that took place over the course of the 19th century — coaches and horses became express trains, letters became telegrams — which makes it “surprisingly relevant to our own times”.

Other aspects of the period have aged worse. The novel ranges over parts of British history that many would rather forget — Cashel serves in the colonial Indian army and explores and “discovers” bits of Africa. Was he worried that his version of history — straightforwardly told, without judgment or apology — might meet pushback from publishers wary of causing offense?

“Absolutely not.” Boyd grew up in Accra in Ghana, where his father worked as a doctor. To this “strange upbringing” he attributes the identity crises that beset many of his central characters and send them wandering through footloose, itinerant adult lives. “My parents were Scottish, but I was born in West Africa. I felt more at home in Accra and Lagos than I did in Edinburgh or London.”

His childhood left him with plenty of first-hand impressions of British colonial rule. He points to moments in The Romantic that directly portray “that futile, arrogant colonialism”. He smiles. “I’m probably as right-on as anybody.” He isn’t sure, however, that A Good Man in Africa, about a secretary to the British High Commission in a fictional West African country, would find a publisher today, even though “all the bad guys get a hard time”.

Boyd is one of a generation of particularly successful and prolific British novelists — Granta’s 1983 list of the best young British novelists names him alongside Martin Amis, Pat Barker, Julian Barnes, Rose Tremain, Salman Rushdie, Kazuo Ishiguro and so on. By chance, Boyd’s novel came out a few weeks after Ian McEwan’s 17th — “He’s had a bit of a head-start on me, but I’m catching up,” Boyd says with a chuckle.

Boyd is still in touch with several of this group — “I’ll send one or two of them an e-mail from time to time. We’re always very pleased to see each other” — but contends that “I don’t measure myself against my contemporaries and I don’t think about posterity”.

“My parents were Scottish, but I was born in West Africa. I felt more at home in Accra and Lagos than I did in Edinburgh or London.”

Really? In his “biographical” fiction Boyd returns again and again to the pathos of legacy, to the meager handful of possessions even the longest, richest lives leave behind. He is haunted by the idea of his books going out of print, as is already happening to some of his contemporaries on that Granta list (Clive Sinclair, anyone?). “You don’t have to wait until you’re dead for your reputation to disappear in a puff of smoke. You can witness your own decline.” I’m not the first journalist Boyd has expressed such fears to.

For the moment, he’s fine — he likes, and very fairly, to make the point that his work is in print all over the world. Yet the fear casts an interesting light on Boyd’s frenetic output. His work in film and television, and the money it brings, is partly a recourse against putting “all my eggs in the novel basket”, even if scriptwriting is “kindergarten level” compared with the freedoms of the novel. The economics of publishing are much tougher than when he started out, after all. “If you don’t sell, you’ve had it.”

Film also brings Boyd into the company of actors, which he loves — he once introduced Sean Connery to Daniel Craig in Edinburgh, which was “perhaps the only time when the two Bonds met”, although Craig’s Bond was still in the future.

He has written a Bond thriller, Solo, published in 2013, and is returning to the spy genre with his next novel. “Everything in the life of the spy applies to everybody’s life. We’ve all betrayed people, lied, we’ve all pretended to be people we’re not. I think that’s why the genre is so appealing because actually you’re writing a novel, but you’re turning up the volume on it.”

He has entered his eighth decade, but Boyd’s voice continues to be heard.

Susie Goldsbrough is the assistant literary editor at The Times of London