Early on in The Girl Next Door, Ruth Rendell gives the reader a sharp nudge. ‘Colin Quell had very little interest in people, what they might think, how they might act in the future.’ The novel is Rendell’s latest stand alone mystery, the uninterested Quell its detective inspector. Forcibly she announces that neither physically nor temperamentally is this Wexford territory. Quell’s stomping grounds are the outer suburbs of London, where the capital spills into Essex, specifically Loughton, where once the octogenarian Rendell herself attended the County High School.

In the present day, though not at the time of the novel’s buried crime, Loughton lacks the residual rural outlook of Wexford’s Kingsmarkham, itself inspired by Midhurst in West Sussex. Its mesh of streets and manicured green spaces suggest suburban introspection, the very setting for Quell the incurious.

That The Girl Next Door works as a standalone novel is partly attributable to Rendell’s deftness in parrying comparisons with her best-known creation. It also unravels a satisfying mystery, stretching tentacles into the past. Rendell appears to revel in the quirky valetudinarianism of her cast of ageing friends and lovers who are capable of ‘iron control’ and equivocation in the matter of changing speech patterns.

For the diehard Rendellian, however, 2014 is the year of Wexford’s 50th birthday. Half a century ago, John Long published From Doon with Death and introduced to the reading public the detective Rendell afterwards qualified as a ‘big ugly man’ and named after a recent holiday destination in the south of Ireland. Wexford was taciturn, sardonic and intolerant of fools. Happily for the law-abiding citizens of his particular patch of Sussex, he was prone to ‘feelings… about some small thing when a case was about to break, and the small thing always turned out to be vital and his hunch seldom wrong’. His subsequent fictional career celebrates the wonderful insightfulness and accuracy of those small hunches.

Rendell later lamented that Wexford was ‘born at the age of 52’, but successfully postponed his retirement for more than 40 years. As readers of The Vault and No Man’s Nightingale will know, retirement has in fact done little to clip the former DCI’s wings: where there’s a will on the part of a crime writer, there’s clearly a way for her sleuth. In his character, the big ugly man contains elements of Rendell’s father: he is also a fictional alter ego of the writer herself. The only threat to Wexford’s ever-active brain and invincible curiosity is Rendell’s own retirement, of which, as The Girl Next Door proves, there is thankfully no sign.

Typically fiction writers tire of their most successful creations, crime writers apparently above all. In her afterword to the anniversary edition of From Doon with Death, Rendell admits to altering her initial conception of Wexford once she realised his probable longevity: ‘If I was going to live with this man, I wanted him to be more literate, more liberal, kindlier, more sensitive.’ This rounder, more fully developed Wexford battles his weight (the lure of Danish pastries defeats him in Harm Done), revels in mixed metaphors and embraces sexual equality in his marriage to Dora, disdainful of ‘the attitude of mind that regards people as things and marriage partners as objects’.

He reads omnivorously, from Kipling to Newman, with a fund of Shakespearean tags that contrive never to seem contrived (perhaps because he worries that his preference for classical music and classic literature is actually ‘a pretentious sham’). His sensitivity to nuance is as acute as that of a terrier to scent; and his strongly developed aesthetic sensibilities are consistently unfrightening to the horses and that stereotypical British attitude that resolutely mistrusts intellectualism or ‘artiness’. It is Wexford’s younger (preferred) daughter Sheila who becomes an actress. At intervals we are reminded that there is nothing of the showman about Sheila’s father: his role as policeman is both absorbing and fulfilling.

By current standards, his bookishness is marked. It is part and parcel of Wexford’s remarkable capabilities and what his sidekick Mike Burden labels his superhuman memory that he can work seven days a week when need be, read widely and retain a sizeable quantity of that reading. Evidently Wexford’s self-assessment in An Unkindness of Ravens that ‘nothing much came along to disturb his private peace’ hits the mark.

The combination of the ordinary and the extraordinary is a powerful one. Aware of the continuing place of class in British society, Wexford is himself a largely classless figure, polite, considerate, civilised but neither ‘posh’ nor overtly ‘educated’. His liberalism has grown markedly in 50 years. He is unabashedly curmudgeonly about declining standards of manners, articulacy and dress: pudding is pudding, ‘dessert’ something quite different. His technical skills are non-existent and he lavished on the rosewood desk with which he furnished his office at Kingsmarkham police station a degree of love other men reserve for a favourite dog. A souvenir perhaps of that ugliness on which Rendell initially insisted, he has a sharp eye for the finer points of other men’s clothing, without ever aspiring to anything approaching sartorial distinction on his own part. In A New Lease of Death, every detail of Roger Pinero’s ostentatiously costly rig-out is grist to Wexford’s mill.

Ultimately Rendell’s gift to her readership is to have redeemed that nebulous, much-vilified, arguably fictitious demographic pejoratively labelled ‘middle England’. With his Yorkstone fireplace, home extension, enjoyment of sherry and the theatre, unshakeable love of his wife and mingled devotion and exasperation towards his children and, in time, grandchildren, Wexford is a middle-aged Everyman. Or as he himself puts it, quoting Conan Doyle, ‘a man of the solid Sussex breed which covers much good sense under a heavy silent exterior’.

Happily neither Wexford nor Rendell insists on that silence with much conviction, while ‘good sense’ seems an understated description of the unflagging psychological insight which distinguishes these stories.