Posters advertising Julian Barnes's Levels of Life currently greet you as you enter your local Waterstones branch, as the chain's book of the month, and it is stationed next to the tills along with The Sense of an Ending. Yet, strangely, copies of another Barnes book – Duffy, the first of the four crime novels he wrote pseudonymously in the 80s – are not there nudging you, although (presumably not by chance) the reissue is also out in April. This, and the fact that the novels written by Dan Kavanagh are coming out without any promotion from Barnes, reflect his wry aloofness from them. At julianbarnes.com, there is "a complete listing of books written by Julian Barnes", with a link to a separate site for "books written by Dan Kavanagh", as if he were a rackety, scapegrace friend or lodger he's often bafflingly confused with rather than an alter ego. (Contrast with the "Ruth Rendell writing as Barbara Vine" approach to pen names, or John Banville's eagerness to promote his crime series.)

Following the link to dankavanagh.com – which features two blurred "alleged photos" – reveals that the creator of the bisexual sleuth Duffy was born (like Barnes) in 1946, in (unlike Barnes) County Sligo and, after an adolescence devoted to "truancy, venery and theft", travelled the world taking such jobs as "a steer-wrestler, a waiter-on-roller-skates at a drive-in eatery in Tucson, and a bouncer in a gay bar in San Francisco", before settling in north London, probably in the 70s. How he's spent the decades since then – and indeed whether he's still alive – is not divulged.

Barnes seems to have talked about the novels, which plunge into the un‑Barnesian milieux of a red-light district, an airport, a football club and a country house, only in an unusually unguarded interview when Duffy first appeared in 1980. It took nine days to write, he revealed, and turning into Dan Kavanagh was "liberating in that you could indulge any fantasies of violence you might have" ("I hate cats," he added, and said that, in a Julian Barnes novel, "I doubt whether I'd do more than lightly push one off my lap, but give me a pseudonym and I'll have one barbecued by the end of the first chapter").

Since then he's kept mum, the books have gone out of print and, even though they're returning, there's a risk the series' significance will be overlooked. A detective who was other than heterosexual or asexual was very rare indeed in 1980 – particularly on this side of the Atlantic, particularly if he was a man; Val McDermid's lesbian journalist-sleuth Lindsay Gordon, often seen as a breakthrough, only made her debut in 1987, the year of Duffy's swan song.

Also notable is their role in restarting the tradition of the literary or non-crime novelist with a crime sideline, which, after flourishing in the mid-century years – as exemplified by Cecil Day-Lewis (Nicholas Blake) and Gore Vidal (Edgar Box) – had fallen into abeyance. Post-Kavanagh, it seemed like a good idea again, and Barnes's example has been followed by Banville (Benjamin Black), JK Rowling (Robert Galbraith) and, most impressively, France's Pierre Lemaitre, the joint winner of last year's CWA international dagger for crime fiction, and, four months later, the winner of the Prix Goncourt.