Irvine Welsh, I think it’s safe to say, is not a writer who’s mellowing with age. His latest book sees the return of ‘Juice’ Terry Lawson from the novel Glue and the short story ‘I Am Miami’ — now an Edinburgh taxi-driver in his mid-forties but still, in the face of some competition, possibly the most priapic character Welsh has ever created. With a penis he understandably nicknames ‘Auld Faithful’ and an unshakeable faith in the power of porridge (‘Complex carbs: set ye up fir a day’s shaggin’), Terry begins his latest adventures by pulling a grieving relative at a funeral — and, on the way home afterwards, two young American tourists. At one point he does go to a sex-addiction meeting, but only in the belief that the women there are guaranteed to be up for it.

No wonder that for a while A Decent Ride looks as if it might resemble an extended prose version of Sid the Sexist from Viz comic — except that Terry’s chat-up lines (‘Ah’m hung like a pit pony that wisnae shy in foalhood when the carrots wir gittin dished oot’) appear to work. Fortunately, while you’d be hard pressed to call this a subtle novel, it does turn out to be far more than that.

There is, for example, the awkward fact that Terry is extremely good company: funny, often quite kind and with a genuine, if highly individual, sense of morality. (In one scene, he talks a young woman out of suicide — and only partly because ‘Naebody in thair right mind wants tae see good fanny gaun tae waste.’) He can even be touchingly sentimental:

Whenever ah walk down they old closes ay the Royal Mile… ah git aw caught up in the romance ay the history ay it aw. Ah think ay the generations ay knee-tremblers that must have took place in this labyrinth.

But the book has plenty of other characters and plots too — including a stereotyped American businessman on the quest for a rare whisky and, more successfully, Wee Jonty MacKay, a uxorious loser unaware that his wife’s a prostitute. All concerned duly get their turn at narrating, with the Edinburgh characters once again writing in what now seems less like Scottish dialect and more like Welsh’s own astonishingly supple invention: one that can combine scabrousness and lyricism, comedy and ruefulness in the same paragraph. (As ever, the standard-English sections, whether deliberately or not, feel distinctly prissy by comparison.)

To call the result a bit of mess certainly wouldn’t be unfair. On the other hand, the last thing you’d want from Welsh is an elegantly crafted novel. Instead, this one seems an almost defiant restatement — even celebration — of his familiar themes, subject matter and techniques, complete with hair-raising proof that he can still think up scenes more gleefully revolting than anybody else around. Readers looking for literary decorum or flawlessness should definitely look elsewhere. If, however, you fancy an authentic and often thrilling blast of full-strength Irvine Welsh, then you’re in for a treat.