The Immortalist is a wildly stimulating, mildly disturbing duologue in the form of a television interview with a man who refuses to die.

With the exception of myself and a few others of my ilk still circulating, every human being ever born on this planet has been murdered, consented to be murdered and spent their entire lives preparing for that pointless little spurt so beloved by footling existentialists. It’s time for Life and Death to get divorced, maybug. What is more revolutionary than the conquest of death? Marxist-Leninist misery? Property is theft? I bet you two shillings to a toffee apple Proudhon couldn’t nick a packet of spam out of Safeways.

I first read it two years ago, when Heathcote called round to see me with a typescript copy. On leaving my house, he was immediately arrested by two policewomen who (he claims) duffed him up and accused him of being drunk in charge of a bicycle. I found myself a key defence-witness at his trial, a long-drawn-out and solemn affair at the end of which he was acquitted. I first saw it acted a year later at the National Theatre of Frestonia – the name given to two streets in North Kensington which, threatened with demolition, had declared a sort of UDI in the manner of Passport to Pimlico. It has since been performed in various places, most recently at last month’s Edinburgh Festival.

Visitors to the Festival also had the chance of seeing Heathcote play the part of Prospero in a film version of The Tempest directed by Derek Jarman. ‘Isn’t that bit about me breaking my staff and drowning my book supposed to be rather important?’ he asked me. ‘Well, Derek said he had trouble fitting it into his conception of the play and I think it’s been cut.’ Nonetheless, Heathcote’s performance was praised in the Listener as ‘melancholically smouldering’ – and he might indeed be considered a kind of Prospero to the alternative society (although his personality contains a touch of Ariel’s volatility, too, with possibly just a dash of Caliban’s balefulness).

Since his startling debut in 1964, when he was only 23 and his brilliant book The Speakers attracted the admiration of Harold Pinter, William Burroughs, Anthony Burgess, V.S. Pritchett and more, he has gradually achieved the status of super-wizard in a community of nomads, pilgrims and seekers after truth. For two years he successfully ran the Ruff, Tuff, Cream Puff Estate Agency (founded by Wat Tyler in 1381) which advised the homeless on suitable premises to squat. (I remember being taken aback, on receiving the agency’s bulletin, to find my brother’s house listed in it with the sinister comment: ‘No apparent security between 11 and 12 p.m.’)

Soberly cycling round his domain on Notting Hill, surrounded by the peeling remnants of his own ‘wall paintings’ (graffiti which have long been accepted by local residents as permanent landmarks – ‘Squat now while stocks last,’ ‘A woman without a man is like a fish without a bicycle’), Heathcote seems to occupy the centre of a charmed circle.

His relationship to ‘magic’ is of two kinds. He is a skilled conjuror whose tricks have diverted many a geriatric ward (although an attempt to levitate his daughter China on the stage of the Lyttelton Theatre was less successful, and a defiant stab at fire-eating landed him with severe burns in a hospital bed beside a patient with gangrene of the testicles). But he is also receptive to magic in its more literal sense, apparently willing to believe in almost anything, from UFOs to the fairy photos that fooled Conan Doyle.

With his Kirlian Camera he has photographed the aura of a 50p piece (Heathcote is no friend to metrication) and found that it resembles a congealed bat’s fart. His restless intelligence makes him impatient with logic and he is drawn to overstatement by a genuine indignation mixed with a teasing sense of farce; he celebrates the irrational in a facetiously punning language with evangelical and apocalyptic overtones.

Clean your spark-plugs, Nosferatu Nerdniks. Ye that are heavy-laden, rip off your clothes, rise up and bathe the world in light. The Recording Angel’s got a polaroid. Where’s the Kirlian clapper boy? Akashic flashers, unsheathe your auric fronds and let it all hang out so far you gotta pump air into it. Click. Click. Take infinity! … Crown King Thing. The aura bomb has been detonated. Our energy is continuous and immortal …

And so on – when he hits this vein, Heathcote can keep it up indefinitely. But in his best work – The Speakers, and four of his plays – the whimsical gift of the gab is disciplined by a basic sense of dramatic structure to produce an effect combining lethal accuracy of recorded speech with vertiginous imaginative flights. His study of the Hyde Park orators might have been taken as a masterly piece of reportage when it came out 15 years ago; rereading it today, one can more easily recognise in it the germs of an exuberant creative gift. The critics who praised it so highly were far-seeing: it still has the staying power of a classic. (A dramatised version, staged in 1974, was worthy of the original.)

Heathcote’s first play, The Local Stigmatic (1965), is a short, chilling drama about two drop-outs obsessed to the point of unbalance by the media’s fabrication of phoney celebrities; they recognise a minor actor in a pub, follow him out and savagely beat him up. This theme is elaborated in AC/DC (1970), a full-length play of dazzling invention and overwhelming power. Both works, considered obscure and unnecessarily violent by many people at the time, now seem to have been uncannily prophetic of the Manson murders. ‘What were the Manson murders about?’ said Heathcote in an interview.

You could say they were about somebody trying to get his songs published: a grub under the blanket of the Great Society. The explanation is that there are two tribes: those who are undernourished in terms of tribal approval, and those who are so overnourished that they become severely debilitated … The point is that Attention is a basic human need like food or sex. No child develops without it, and if you don’t get it you wrinkle up. And as the media stand now .0001 per cent of the population is getting crème brûlée every day, and the rest are being ignored.

In AC/DC Heathcote furthered the investigation into the speech rhythms and thought patterns of schizophrenia which he had begun with the character of MacGuinness in The Speakers, unnervingly relating paranoid delusions of ‘electronic control’ to the actual developments in technological progress which underpin our lives. Ending with a trepanation scene performed onstage, it is a very frightening play, and perhaps it frightened Heathcote. Certainly Hancock’s Last Half Hour (1977) – a witty, melancholy monologue leading up to the comedian’s suicide in an Australian hotel-room – reverts to a more humanist theatrical tradition, while The Immortalist recalls the dialectical device exploited by Diderot in Le Neveu de Rameau.

Since 1970, Heathcote’s serious writing for the theatre has become marginally mellower in tone while his propaganda pieces grow more outrageously scabrous. At the time when he was inveighing against famous people as psychic capitalists getting their astral projection on the cheap, he fell in love with the most famous model in the world, Jean Shrimpton, and lived with her for several years. I assume that this item of personal history may be mentioned without impertinence, because Heathcote has published, next to a mutilated photograph of Jean, a virulent exercise in loathing called Polythene Pam which rivals Céline’s lunatic ravings against the Jews in its intemperate nastiness. It is clear that what Heathcote hated was himself for ever having paused from hating what she represented.

So he is a creature of extremes. Of conventional upper-middle-class origin (educated at Eton, father a QC – ‘just like Rumpole’, mother a clergyman’s daughter), he excels at writing about alcoholics, schizophrenics, junkies, tramps. Accidentally contemporary with such movements as flower power and the drug culture, he became in a sense their Savonarola, embracing their cause with a passion, energy and rigour conspicuously lacking in their other devotees. Possessed of a remarkable intellect, he takes a perverse pleasure in giving credence to the most farfetched rubbish he can find. Gentle and generous in life, he can be spiteful and violent in print. By the same token, endearingly muddled as a companion, he can rise in his plays to heights of piercing illumination that make one think of Rimbaud.