“Left to their own devices, the natives would rely on nothing but the instant carbohydrate gratification of the plantain.” These are the words of acclaimed journalist, former Major of London, and so-called “national treasure” Boris Johnson. How this casually offensive toff was ever considered loveable, let alone respectable, will be the wonder of future historians.

Meanwhile, it appals another old Etonian, Heathcote Williams, who has devoted much of his life to undermining an establishment that he knows first-hand – and not as a bien pensant bourgeois, but with real action and anger. A poet, playwright, squatter, magician and more, he has now focused all his fury and wit in a lacerating take-down of supposedly loveable Bojo.

The Beast of Brexit: a Study in Depravity is a pamphlet in the radical, Swiftean tradition of pamphleteering revitalised by Williams and his contemporaries in the Sixties – and still remarkably robust – and this 20,000-word collage of the most maniacal, hypocritical, and cruel things the former mayor has ever said or done makes for electrifying reading. It has even been declared “book off the week” by the influential London Review of Books.

Why? Because, although many of Johnson’s exploits are widely known, Williams has a poet’s ear for the damning and often neglected specifics. By the end of the diatribe, you can’t avoid the conclusion that Johnson is a terrifying sociopath. As for Brexit, that’s not really the issue in this slim volume; nor, says Williams, does Johnson really care about its likelihood. Bojo’s intention, he says, is only to “bounce his 17-stone self into Number 10 Downing Street”.

Here, we read of Journalist Johnson’s carelessness with the truth: from falsifying quotes by his godfather Professor Colin Lucas to sexing up a story about an archeological discovery, to inventing an EU plot to ban dipping bread in olive oil. We encounter his fair-weather loyalties: passionately supporting then-President George W Bush until it suited him to recast Dubya as “a cross-eyed Texan warmonger, unelected, inarticulate, who epitomises the arrogance of American foreign policy”.

Here we’re reminded of his cruelty towards women and the violence in his personal life. We observe his love of the super-rich, whom he once described as “a put-upon minority like Irish travellers and the homeless”.  And let’s not forget his friendship with the fraudster Darius Guppy. Would Boris get the address of a prying journalist, so that Guppy could have him beaten up? Sure, said Johnson.

None of which may have much bearing on the future of our pensions or the straightness of bananas. But then, the book’s title – or its first half, at least – is just a peg, conveniently provided by West End, his German publisher. Four years ago, to coincide with the Queen’s visit to Berlin, it published in translation his last major essay, an anti-monarchist polemic called Royal Babylon. “And for that,” Williams says down the phone from Oxford, “I felt a certain obligation to do something specifically for them. But then they asked me to write about the referendum! The idea of writing anything about Europe and Brexit filled me with an earthquake of a yawn.”

Williams’s speech is littered with dramatic turns of phrase, his (now raspy) voice precise in its pronunciation, as he describes how he managed to make the political personal. “The poet Niall McDevitt turned me on to an impending attack”, signed off by Johnson while he was still mayor – namely, the desecration of Bunhill Fields in the City of London; now a public garden, once a burial ground and still the resting place of the visionary William Blake, the patron saint of the English mystic tradition.

“He essentially wants to surround them with these venal tower blocks filled with City slickers, casting a shadow on the anti-materialistic Blake. That really got my goat. It was a step too far,” says Williams. “There’s a German word for people like Johnson: Backpfeifengesicht. It means ‘a face that needs to be punched’.”

Boris Johnson’s sole aim is to become Prime Minister, according to Williams (PA)

As this point, I must admit a complicated relationship with my subject. Although friends with my grandfather, there was no family connection. I was named, if you like, in tribute, after my mother was deeply moved by Williams’s 1988 Whale Nation – a disorientating paean to the largest mammal on earth, and aching reflection on the destructiveness of humanity. I didn’t meet him until later in life, but was reminded of his existence almost daily by people asking: “Where’s that funny name from, then?” There was never a shortage of material with which to answer.

In 1964, the 23 year-old Williams published The Speakers, a surreal ethnography of London’s most famous public ranting spot, Speakers’ Corner. It earned praise from Samuel Beckett, William Burroughs and Harold Pinter (the last of whom wrote: “These are the only people I’d ever want to listen to”). Pinter commissioned him to write a short play, which was to become The Local Stigmatic, later made into a film by Al Pacino, and recently revived at the Old Red Lion Theatre in London for its 50th anniversary.

His first full length play AC/DC premiered at the Royal Court in 1969 and elaborated on its predecessor’s theme of the grotesque inequalities caused by celebrity culture. (“Part comedy, part visionary tract, part psychedelic nightmare,” wrote The Guardian’s reviewer.) Many more gems were to follow, including the poignant Hancock’s Last Half Hour, and there was always a flow of pamphlets, poetry and manifestoes.

Throughout the Sixties and Seventies, Williams furiously involved himself in London’s counterculture – on which he left an indelible mark – and his experiments with alternative lifestyle were just as important as his writing, at least in terms of reputation. He was obsessed with magic, and briefly a member of the Magic Circle. (“I think it’s just breaking rules, really,” he says. “Magic gives the illusion of breaking rules, about gravity, about time, about place.”) And in the first-ever London Review of Books, Francis Wyndham wrote “The Magic of Heathcote Williams”, a piece that hailed him as “a kind of Prospero to the alternative society”.

“He is drawn to overstatement by a genuine indignation mixed with a teasing sense of farce,” continued Wyndham. “He celebrates the irrational in a facetiously punning language with evangelical and apocalyptic overtones.” Williams’s domain was Notting Hill, which was liberally daubed in the poetic graffiti of his milieu. “Squat now while stocks last”, “words do not mean anything today” and “housing is a right, freedom is a career” are some choice classics.

He worked intermittently and chaotically on different magazines: the literary journal Transatlantic Review, the radical vegetarian magazine Seed, and animal rights magazine The Beast (“the magazine that bites back”). Along with Germaine Greer and others, he founded Suck – the first European “sexual liberation” paper – before going on to establish “the independent state of Frestonia”, a squatted neighbourhood in West London’s Latimer Road.

Frestonia applied for a tank from the UN in order to defend itself from the local council. “It was a ploy really,” he says. “We had our own passports, our own stamps. The idea was to firewall these streets with so much publicity – à la the Ealong comedy Passport to Pimlico – that they would have to give us concessions. And it worked. A lot of people got social housing out of it.” Meanwhile, they had their own ministers and passports; walls were knocked down to make the back gardens collective; they took over a defunct local hall and turned it into their own national theatre. “In a way, I suppose that was a Brexit of sorts. That’s the kind I would like, not that of Boris Johnson.”

In the mid-1970s, Williams spent two and a half years running the Ruff Tuff Cream Puff Estate Agency. They would crack empty buildings, change the locks and give the keys to anybody in need of a house. It has been estimated by Tony Allen, the “father of alternative comedy”, that the agency was responsible for housing thousands of people (including a young Joe Strummer). After market days, leftover vegetables would be collected in a cauldron and served as Rubbish Risotto or Portobello Soup. “We were seeing people whose homelessness had caused other dark conditions. Somebody knifed me in the stomach for no reason at all. It was quite hairy sometimes.”

It was rumoured that the police were gathering evidence and intending to charge Williams with whatever they could in order to send him to prison. Mindful of the heat, he got out of town and in the next two decades wrote his best known works, a trilogy of richly illustrated book-length poems on environmental themes. After Whale Nation came its elephant equivalent, Sacred Elephant (1989), and then Autogeddon (1991), a Ballardian reflection on how cars are taking over the planet:

If an alien was to hover a few hundred yards above the planet

It could be forgiven for thinking

That cars were the dominant life-form,

And that human beings were a kind of ambulatory fuel cell:

Injected when the car wished to move off,

And ejected when they were spent.

The following 20 years passed more or less in obscurity and illness. “I wasn’t just lying around” he says, slightly defensively, “I was painting and writing. I campaigned to save Jericho Boatyard in Oxford from property developers.”

More recently, he helped to re-launch the International Times (founded 1966), both online and as a print publication that has so far run to three issues. And in the renaissance editorial, he invoked a spirit that has as much relevance to many young people now as it did nearly 50 years ago:

“One minute IT was a soggy-brained psychedelic hippy, the next a member of the Red Army Faction. It was a paper that endorsed squatting while the entire UK mainstream media liberal ‘lifestyle’ papers such as The Guardian were petrified by it and demonised it. The hidebound Marxist Left regarded IT and all it stood for as hedonist adventurism. So it was. And is. And much besides.”

But now Williams has come out of hiding, what’s next for the croaking old sage? “I’m working on too many things to mention, actually. My head is littered with unfinished stuff. I prefer talking about things when they’re cooked.”

Heathcote Williams’s pamphlet ‘Boris Johnson: The Blond Beast of Brexit A Study in Depravity’ is available from the London Review of Books bookshop for £7.99, tel: 0207 269 9030