There is a great tradition of British spy fiction, just as we have an equally strong lineage of our real-life operatives betraying, and being betrayed in turn. Perhaps there is something about our cold, wet country that lends itself to the image of a lone middle-aged figure, clad in a mackintosh and spectacles, patiently standing on a street corner as it drizzles gently as he carefully observes passers-by while waiting for a letter drop or some nugget of information to be discreetly passed his way. While most accounts of espionage focus on how boring it is, and how little reward is obtained from endless effort and time spent ‘in the field’, a great writer can make the entire subject fascinating, as well as skilfully bringing in political and social analogies that turn our security services into a microcosm of contemporary England.

This literary tradition stretches back as far as Conrad and Kipling, and was popularised by Graham Greene in such novels as The Confidential Agent and Our Man in Havana, but John le Carré and Ian Fleming, in entirely different ways, both produced what have come to be seen as the definitive and most influential works about espionage. They respectively revolve around the careful, low-key figure of George Smiley and his investigations at the Circus and the flamboyant, womanising secret agent James Bond, licenced to kill and to drink heavily. It functions as a kind of Rorschach test for a spy novel aficionado as to who they regard as the ‘classic’ spy, Smiley or Bond, often with the unspoken proviso that as many readers would seek to emulate the careful, brilliant older agent as the younger, flashier one.

Yet now the writer Mick Herron has written a series of novels that nod to both progenitors, as well as Greene, but has made them decidedly contemporary. There is a central character who has loose similarities with Smiley, just as another is not a million miles away from 007, but neither Fleming nor le Carré were quite so irreverent about the genre, or espionage itself, as Herron is. Thus his version of Smiley is Jackson Lamb, the obese, flatulent and obscene capo of his crew, and his interpretation of Bond is River Cartwright, a hot-headed young man who has to be rescued from dire situations with amusing frequency by his more competent (and usually female) colleagues.

Lamb, Cartwright and the rest of the denizens of Herron’s universe – the so-called ‘slow horses’ – inhabit Slough House, which is a kind of espionage version of Father Ted’s Craggy Island. This is portrayed with some relish as a run-down, grubby and disreputable establishment in the City of London where those who have somehow transgressed have been exiled to. Most have been summarily expelled from ‘The Park’, the palatial surroundings of Regent’s Park where, in Herron’s telling, the ‘real’ MI5 is headquartered.

Their misdemeanours, which include everything from drunkenly mislaying sensitive documents on the Tube and accidentally evacuating King’s Cross at rush hour to alcoholism and a gambling addiction, have seen them condemned to careers in wearying admin, endlessly checking CCTV and dealing with the boring donkey work that their more successful colleagues are spared. Little wonder that they are known, contemptuously, as the ‘slow horses’, the name both a pun on the quarters in which they are domiciled and the undemanding, enervating labours that they undertake.

It is not spoiling the storylines to reveal that the residents of Slough House do not sit listlessly in their horrible building throughout the novels, but instead find themselves taking part in often blackly comic and violent exploits with a variety of foes and nemeses, which allows Herron to smuggle a strong vein of satire into his often blisteringly exciting action scenes. One of the major characters throughout the saga is Peter Judd, the manipulative, priapic and conscience-free Home Secretary, ‘a loose cannon with floppy hair and a bicycle’, who of course bears no relation to any politicians active today, just as it remains a pure coincidence that Herron was at Balliol at the same time as Boris Johnson. There is a punkish, anti-authoritarian spirit throughout the books that sits amusingly with its depiction of this band of civil servants tasked with keeping the country safe. Given that they can barely stand one another, working alongside one another to thwart wrongdoers seems like quite the ask.

He is a character of Falstaffian complexity and richness

The heart of the saga remains Lamb, so much so that the books are now billed as ‘Jackson Lamb thrillers’. He is a character of Falstaffian complexity and richness, a former Cold War operative who has apparently settled into boozy cynicism as master of Slough House. Herron sets great store in lengthy descriptions of Lamb’s questionable personal hygiene, his gluttony and casually dismissive attitude towards his underlings, not least the technical expert Roderick ‘Roddy’ Ho, whose patronising mansplaining comes in for some of Lamb’s (and Herron’s) most trenchant one-liners, seasoned with a lack of political correctness.

Yet Lamb is also a superlative field agent, possessed of razor-like acumen, a deeply developed moral code and a protective instinct towards his staff, or ‘joes’, which is best expressed when one of them is endangered or injured. He dominates every scene that he is in, and is one of the most memorable characters in contemporary literature. The success of the books is that they are just as compelling and readable whenever Lamb is offscreen, too.

As the latest in the series, snappily entitled Slough House, is published to the critical acclaim that every book has been showered with, it is salutary to look at how Herron’s career has progressed. In an illuminating recent Guardian interview, the journalist notes that, far from the usual lavish lifestyle that most acclaimed and bestselling crime authors enjoy, Herron lives in a ‘plain and modest’ flat, and ‘I sense, from our surroundings, that he’s not exactly flinging money about’.

This is not out of miserliness, but simple pragmatism, borne from a late-flowering novelistic career. Herron wrote his first series of books about an Oxford private detective called Zoë Boehm to what might be called respectful disinterest, before switching to write about Lamb and Slough House in 2010. The first book in the series, Slow Horses, was brought out by his then-publisher Constable, but weak sales meant that they did not ask for another in the series. It was therefore firstly thanks to the American imprint Soho Press that the next two, Dead Lions and Real Tigers, were written and published at all, and then down to an enterprising editor at John Murray, Mark Richards, who saw hitherto untapped potential in the books and asked Herron if he could republish them.

Herron, who maintained a day job until fairly recently as a subeditor on a legal journal not a million miles geographically from Slough House, was sceptical. Richards, however, believed in him and his novels, not least because Herron had won numerous awards by this point, including the Crime Writers’ Association Gold Dagger prize for Best Crime Novel in 2013. With his new editor’s encouragement, Herron kept at a level of consistent literary attrition that meant that slowly, painstakingly, the books reached a kind of critical mass by 2017, by which point he had given up his sub-editing and was able to write full-time. Now, Richards’ faith and patience have been rewarded in spectacular fashion. The books are lauded to the skies by critics and readers alike, sell in enormous quantities and is currently being made into a TV series with a starry cast including Kristin Scott-Thomas as the Park’s frosty supremo ‘Lady’ Diana Taverner, Dunkirk’s Jack Lowden as Cartwright and, most intriguingly of all, none other than Gary Oldman as Lamb.

The casting of the famously slim and even ferrety Oldman as the gargantuan, oozing spymaster is an unexpected development, given that one might have expected a ‘robust’ actor such as Ken Stott or Robbie Coltrane to take on the part. (Timothy Spall, who Lamb is compared to physically, has lost a great deal of weight over recent years, so would no longer be obviously suitable, but then again neither is Oldman.) It remains to be seen whether the adaptation will place him in a fat suit and prosthetics, as he famously donned to win an Oscar for playing Winston Churchill in Darkest Hour, but not only will the great actor bring his usual intelligence and intensity to the part, but he will also carry the baggage of his previous fictional portrayal of George Smiley in the 2011 film adaptation of Tinker Tailor Soldier Spy: a suitably neat piece of both meta-cinematic and meta-literary allusion.

One hopes that the series will be as good as the previous le Carré adaptations both televisual and cinematic, but even if it irons out the moral complexities and vivid black humour of Herron’s prose, it should still have the desired effect of bringing in curious readers to the books. They will be in for a treat. Speaking for myself, I read Slow Horses last year on the recommendation of many friends and fellow writers whose opinions I trust, and enjoyed it immensely, though I did describe it as ‘a superbly written genre novel’. I, an entirely hooked reader, now consider this an understatement somewhat akin to calling Decline and Fall ‘a promising first book with a few funny bits’.

One hopes that the series will be as good as the previous le Carré adaptations both televisual and cinematic

The adventures of Lamb, Cartwright, Ho and the rest of the Slough House crew – many of whom are killed off in the most brutal and unexpected of fashions, meaning that one can never rely on one’s favourite characters surviving the book – are one of the highlights of recent literature as far as I’m concerned. You can keep Hilary Mantel, Sally Rooney and, God help us, David Walliams. Every time that the reassuringly prolific Herron publishes another book, the door will be barred to intruders, a glass of something that Jackson Lamb might approve of shall be poured, and I shall settle down for a bracing, hilarious evening of reading the sort of provocative, innovative fiction that, by rights, should be winning the Man Booker as well as the CWA Gold Dagger. And, as one character says of his grandfather, ‘For my twelfth birthday, he bought me le Carré’s collected works. I can still remember what he said about them.’

They’re made up. But that doesn’t mean they’re not true.’