It’s coming up to the 50th anniversary of the non-transmission of Dennis Potter’s TV play Brimstone and Treacle. Yes, non-transmission – because just days before it was scheduled to go out, BBC director of television Alasdair Milne pulled it, stating that it was “nauseating” though “brilliantly made”.

The decision to shelve it came so late that the Radio Times had already gone to the printers, promoting it as the next episode of anthology drama series Play for Today. The BBC eventually relented and screened it in 1987 (five years after an inferior cinema version with Sting), when I first saw it. Nearly 40 years on from that, it remains profoundly shocking.

Before I say why, I should explain the title, which has lost some of its resonance with time. Brimstone and treacle was a real substance, a pre-modern placebo medicine that was a mixture of sulphur and molasses. It is administered by Mrs Squeers to the boys at Dotheboys Hall in Dickens’s Nicholas Nickleby, for example. The phrase came to mean something that seems bad but is actually good for you.

To make sure we get this point, the play begins with a quote from Mary Poppins – “a spoonful of sugar helps the medicine go down”. (Mr Banks was given brimstone and treacle by his own nanny as a child; it’s the title of one of the new songs added to the stage musical version.) Like Poppins, Brimstone and Treacle is the story of an uncanny stranger who lodges with a family and solves their big problem – but in, let’s just say, a strikingly different way.

Sting with Suzanna Hamilton in the 1982 film adaptation – Collection Christophel/Alamy

We meet Martin (Michael Kitchen), a devil (possibly the Devil) in human form, who comes to lodge with middle-aged couple Tom and Amy Bates (Denholm Elliott and Patricia Lawrence). Their young adult daughter, Pattie (Michelle Newell), was the victim of a hit-and-run driver two years before, and has been left in a vegetative state. Martin inveigles himself in with the Bateses, and offers to lighten the load on Tom and Amy by caring for Pattie while they go out for a change. This being a Potter script, Martin regularly talks to the camera and is accompanied by bitterly ironic versions of popular hits of the writer’s childhood such as That Old Black Magic.

Martin takes the opportunity of her parents’ absence to sexually abuse Pattie. He also tries to tempt Tom towards Nazism, and to stimulate the dormant feminine vanity of Amy, encouraging her to go out and titivate herself at a beauty salon (which, perhaps tellingly, the script seems to portray as an equal sin). At the end he rapes Pattie – but is interrupted and flees; after which Pattie is, shockingly, cured. It is surely this scene in particular that led to Milne cancelling the broadcast, though he didn’t explicitly say so.

One of the oddest things about our cultural memory of the 1970s is the idea that TV was all slapstick bums and boobs, minstrels and mother-in-law jokes. In fact, a very large slice of airtime was taken up by weighty, worthy one-off drama. The BBC particularly was churning out socially concerned fare: drugs, destitution and despair, broken windows and bare behinds. After half past nine you were almost guaranteed a Rada-trained junkie saying something like: “Hell, I just need my next fix, Malcolm.”

Dennis Potter was part of that world, but he was, by a country mile, the most interesting part of it. His other works such as Pennies From Heaven and The Singing Detective are similarly inventive and odd and frequently sexually perverse, but none of them – even the embarrassingly personal Blackeyes in 1989 – match the disgusting potency of Brimstone.

Michael Gambon in The Singing Detective (1986) – AJ Pics/Alamy

Because yes, the four performances are superb, and the dialogue is crisp and clever. However, while things may slip in and out of moral fashion, the abuse and rape of a mentally incapacitated person is something that will never be acceptable viewing. These scenes remain almost unwatchable.

Also, Potter can’t help showing that strain of lofty Lefty disdain for ordinary Britons such as the suburban Bateses, that we see in worthy dramas, ancient and modern (in the BBC’s recent Christie adaptations, for example). There is a kind of revulsion at pre-war, pre-welfare state Britain, of blaming the entirety of that society for whatever befell the writer in particular. Of course, the incipient political evil of Tom Bates is Right-wing rather than Left-wing, which would’ve been unthinkable for the BBC, then as much as now.

But we should remember that Potter himself was a survivor of child sexual abuse, a sick man who was in constant agonising physical pain (and particularly so at the time he wrote this, he later revealed). Like much of the work of Pasolini, (whose 1968 film Teorema is remarkably similar), Brimstone is vomit as art, a writer bringing up the horrors of his own life on to paper.

The demonic cuckoo-in-the-nest intruder is done so much better in Joe Orton’s earlier stage hit Entertaining Mr Sloane. The actual devilment in Brimstone is perfunctorily done – you get more effective scares in a bog-standard episode of Sapphire & Steel.

Above all, the play feels like it is goading the viewer – which is never, or hardly ever, a good characteristic of any piece of culture. Think of the art of Damien Hirst, for example. Potter in particular reminds me of George Orwell’s essay on Dalí: “He has 50 times more talent than most of the people who would denounce his morals … perhaps his aberrations are a way of assuring himself that he is not commonplace.”

Provocateur: TV dramatist Dennis Potter was the author of Brimstone and Treacle – Sally and Richard Greenhill/Alamy

Because what Potter did here was the familiar routine of the provocateur – to deliberately spark a reaction, and then complain about that reaction. After Milne pulled the play, Potter snapped back in the New Statesman (of course): “If the best of what is to be forbidden to viewers is the possible nausea and outrage the programme might cause, then how come that in the same drear week that Brimstone and Treacle was due to be shown we had to put up with such proven emetics as Jim’ll Fix It, the 400th repeat of Star Trek, and two uninterrupted hours of the Eurovision Song Contest…?” Potter comes across here as an appalling snob, the epitome of the worthy TV middle class he had become a part of.

With his personal history, it’s perhaps inevitable that Potter would want to scream at society and its institutions. But are we viewers any better off for it? Was Potter any better off for it? On the evidence of his later works, I would suggest no. Speaking as an atheist myself, I think he’d personally have been much better finding a good church than hanging around the BBC reliving all his traumas by shoving them into other people’s faces. In spite of the undeniable genius of some of his work, he might have been better off had he not written it.

At the close of Brimstone and Treacle, have we been enlightened? Do we understand anything more clearly? I don’t think so. Potter said of the play: “We cannot even begin to define ‘good’ and ‘evil’ without being aware of the interaction between the two.” This central point – good things can come from evil things – is banal.

Good drama should get us thinking and Brimstone and Treacle doesn’t, much. As Alasdair Milne said back in 1976, it doesn’t get a sufficiently valuable point across to be worth all of the bother. It is brilliantly staged nihilism, immaculately acted unpleasantness, and that’s all. But oh for a nasty writer of Potter’s calibre working in TV today.