A couple dozen pages into “Clown Town,” Mick Herron’s latest novel, two veteran spies share a bench in London. They’re Jackson Lamb and Diana Taverner, notorious fictional fixtures of MI5, the British intelligence service. Fans of “Slow Horses,” the Apple TV series adapted from Herron’s earlier Slough House books, will recognize the pair as the characters played with brisk professionalism and callused gravitas by Kristin Scott Thomas and Gary Oldman.

Those incomparable actors are a big part of the show’s appeal, but the Britain they inhabit — weary, cynical, clinging to the tattered scraps of ancient imperial glory — is built out of Herron’s witty, corkscrew sentences.

And this bench, like others where Lamb and Taverner meet with some regularity on both screen and page, is hardly an incidental bit of urban furniture. It holds not only their aging bureaucratic bums, but also a heavy load of literary and sociological significance.

An ambient sarcasm hangs in the foul air around his characters. Nearly every word is freighted with a mockery that is indistinguishable from judgment. Herron’s prose bristles with the kind of active, restless grudge against the world that is the sure sign of a moralist.

While spies, bureaucrats and especially politicians come in for comic scolding, the real target of his satire is an administrative regime that will be familiar to many readers and viewers who have never cracked a code or aimed a gun. In interviews, Herron has often noted that unlike John le Carré, to whom he is often compared, he has had no first-hand experience of espionage. But he has spent enough time toiling in offices to understand the absurdity — the banality, the cruelty, the cringeiness — of modern organizational life.

“Slow Horses” is a workplace comedy, and Diana and Jackson — nightmare colleagues and bosses from hell — are its flawed, indispensable heroes. Their nastiness to each other and everyone else is a reflection of their circumstances, but also a form of protest against the ethical rottenness of the system they serve.

The gimlet-eyed Diana, managing up from a precarious perch high in the organization, must contend with the cretinous crème de la crème of the British establishment. The epically flatulent Jackson, a career reprobate exiled to a marginal post far from the center of power, manages down, wrangling MI5’s designated misfits, the Slow Horses who give the series its name. Those poor spies need to be protected from external savagery, internal treachery and their own dubious instincts.

Jackson and Diana seem to share a cynical, self-serving outlook, but what really unites them is that they care enough about the job to do it right. More than that: They may be the last people in London who believe in decency, honor and fair play, embodiments of the humanist sentiment that lurks just below the busy, satirical surface of Herron’s novels. Not that they would ever admit as much — especially not to each other, planted on a public bench, where anyone could be spying on them.