I have never thought of the spy novelists who came after John le Carré as working in his shadow. We are, rather, writing by the light he cast, a light that shone down dusty corridors, illuminating a wealth of grubby detail. In its beam, we see Peter Guillam filching a file from the Service archive; we view the shabby lodgings Inspector Mendel organises as George Smiley’s bolt-hole at the start of his mole-hunt. We meet the underdogs George reaches out to when he begins weaving his net. Le Carré, to use his own lexicon, was a lamplighter, and some of us would be utterly in the dark without him.

There were other spy writers, of course, but le Carré made the territory his own, and in his great trilogy of the 1970s — Tinker Tailor Soldier Spy, The Honourable Schoolboy and Smiley’s People — used the genre not only to examine the ideological battleground of the Cold War, but also to pay witness to the tattered flags being lowered over the empire. His secret pilgrims were civil servants mostly, succumbing to love or treachery almost despite themselves, and hanging on to notions of duty while the establishment did what the establishment does: sold the family silver and forged deals with various devils. And while he was capable of epic sweep, most notably in Schoolboy, it was in intimate and shabby quarters that he excelled, capturing “the last beat of the secret English heart” in whatever dusty corners it could be heard.

That trilogy is 40-odd years old now, of course, which might have been an issue for their author. To have created the greatest spy in fiction, within the finest novels to exist within the genre, and to have done so, moreover, with decades of work yet to come — work that would include A Perfect Spy and The Constant Gardener — might easily have become an albatross round an author’s neck. No working novelist wants it thought that their best is behind them, and I’ve read that le Carré declined to sign copies of his earlier books. Whether that’s true, I don’t know — and anyway, as Kingsley Amis put it, a burden like that is better than having no bloody albatross at all. What’s beyond doubt is that le Carré embraced his past, and Smiley, with the elegiac A Legacy of Spies three years ago. I say “elegiac” — it felt like a farewell. It turned out not to be. Le Carré was always full of surprises.

To mark that occasion, the author made a rare public appearance, at London’s Royal Festival Hall. His performance was magnetic. Without once, that I recall, consulting notes, le Carré talked his way through the life of Smiley, making it clear that, however far his work had taken him from the Circus of the 1970s, George had always been at his side. Their conversation hadn’t faltered.

When I last read Smiley’s People, just over a year ago, I found new things in it. I can’t see that coming to an end. There won’t be any more work from John le Carré — it really is farewell this time — but he’ll still be lighting the way all the same, carrying his lamp into dusty corners.

Mick Herron is the author of the Slough House series of spy thrillers