We’ve all seen Brian Cox playing a fearsome media magnate with a perhaps non-coincidental resemblance to certain real-life figures. But many people won’t realise that his performance as Succession’s brutal patriarch Logan Roy represents the completion of a circle. Back in 1968, when Cox was fresh out of repertory theatre, he landed the role of Lasar Opie, a junior but still pretty ruthless functionary at the heart of an imagined media landscape of the near future. And, although some of Opie’s decision-making might have shocked even Logan Roy, The Year of the Sex Olympics – first shown on BBC Two – does a terrifyingly prescient job of imagining aspects of post-millennial television.

The Year of the Sex Olympics was the brainchild of writer Nigel Kneale. Its forthcoming DVD release represents an act of retrieval: in common with so much television from the era, a colour version of the drama was wiped. By 1968, Kneale’s adaptation of George Orwell’s 1984 and three Quatermass serials had established him as a bleak and questioning small-screen auteur. The Year of the Sex Olympics takes place in a stratified, heavily regulated society in which the majority (known as Low Drives) are pacified by a constant diet of televised pornography produced by the ruling High Drives who control the government and media.

It’s less racy than that sounds; the action had to be sufficiently vanilla to appear on prime-time television in the late 60s. Superficially, the show resembles nothing so much as very early Doctor Who. But, although it’s visually clunky at times, the physical, linguistic and behavioural world-building is convincing on its own terms, while the subject matter is smart, even revelatory. As Cox puts it in his engaging DVD commentary: “It’s chilling, when you think about it, how prophetic this piece is.” As the narrative unfolds, the echoes of television – and society – in 2020 become unsettling.

It’s tempting to simply list the modern pathologies anticipated here that are all perceptively examined: the desensitising effects of porn, the invasive voyeurism of reality TV, the passivity of mass consumerism, our sensitivity to “triggers” and sometimes unhealthy attachment to safe spaces, our conditioning to advertising and urbanised humanity’s disconnection from nature. Matching a trajectory that will ring grimly familiar to observers of everything from Big Brother to The Jeremy Kyle Show, the effect of this unbalanced TV diet on its consumers is stupefying and eventually deadening. The Low Drives cease to react to porn. Something more “real” is needed to tickle their jaded palates. At which point Lasar Opie has an idea with alarming implications.

The horror of the drama is very human and, as subsequent years have demonstrated, all too believable. Kneale was an atheist with no belief in the supernatural. Instead, The Year of the Sex Olympics was about the horror humanity might be capable of inflicting on itself. As the daughter of dissidents inside Nazi Germany in the 1930s, Kneale’s wife, the children’s writer Judith Kerr almost certainly influenced his worldview. Kneale is clearly interested in the lexical and, by extension, imaginative implications of mass hypnosis. In The Year of the Sex Olympics, the characters’ communication has de-evolved. They speak in a sparse, detached argot that suggests a twee, baby-talk version of Nadsat, the teen-gang language in A Clockwork Orange. This is a language reduced to basics. It has lost its descriptive precision because society’s horizons have become so limited. The food is protein sticks, the setting is entirely sheltered; basic human notions of discomfort (cold, hunger, pain) have been banished, but so has joy.

Eventually, this self-limitation has practical implications. As the drama’s climax approaches and a couple of the High Drives find themselves stranded in the outside world, it becomes clear that they no longer possess the apparatus for processing complex challenges or emotions. The word “love” is impossible to locate. The concept and properties of fire elude one character with blackly comic consequences. In his 2015 book, Landmarks, Robert MacFarlane wrote about the diminishing of the “word hoard” as words relating to nature were nudged aside in children’s dictionaries by ones connected to technology. Back in 1968, Kneale appears to have seen this coming.

The film is admirably ambiguous; simultaneously a celebration of the freedom of the era that spawned it and a warning about potential unintended consequences. In his commentary, Cox ponders the paradoxes of the time. “The sad element of the 60s was that we weren’t able to take it forward,” he notes. “We didn’t have enough real visionaries. It was a lost opportunity; in these islands at least, one that we’ve never regained. I think in a sense, all the woes and the way the media has deteriorated stems from that. We’re always so involved with our own time but you do need the prophets, the visionaries to progress.”

Like most visionaries, Kneale wasn’t easily forced into a particular political or philosophical category. Inevitably, anti-obscenity campaigner Mary Whitehouse was a fierce opponent of the film and attempted to prevent its broadcast. And yet, if she had actually given it a little serious consideration, it’s not impossible that she might have found some common ground with its moral position. “Inhibitions are like the bones in a creature,” Kneale once said in reference to permissive hippy culture. “You pull all the bones out and you get a floppy jelly.” There’s a moral rigour at the heart of The Year of the Sex Olympics that feels anything but decadent.

Reviewing the drama after broadcast in the Guardian, Nancy Banks-Smith sensed its prescience. “The play radiated ripples,” she wrote. “Is television a substitute for living? Does the spectacle of pain at a distance atrophy sympathy? Can this coffin with knobs on furnish all we need to ask?” The continuing pertinence of these questions is striking. And Cox recognises it, too, perhaps shuddering as he considers a media-scape full of Logan Roys.

“It’s so important to see our history,” he says, “and how fast our evolution is on some levels and yet how slow it is on others. We depend on the media more and more and yet it’s becoming more and more distorted and hard to believe. This programme predicts all of that.”

• The Year of the Sex Olympics is available on DVD now.