Mr McKenna contends that hallucinogenic fungi inspired our primate forebears to develop language, boot-strapping us up the evolutionary ladder to the brink of self-
realisation, and that this humble mushroom is now ready and waiting for us to complete our ontological correspondence course, if we would only tear ourselves away from smack, crack, coke, caffeine, tobacco, alcohol, sugar, cocoa, uppers, downers and all the other bad substances we are addicted to.
He believes that hallucinogenic- plant gnosis is the lost key to our intellectual, moral and spiritual development as a race; that all subsequent drug abuse is merely an attempt to satisfy our primal urge for psychedelic union with nature ('an itch we cannot scratch'); and that cataclysmic change or certain extinction awaits us. His theory states: 'No perception without hallucination.'
We are in a small house in west London. There are 40 people sitting on cushions around the room, which is large and airy, full of plants and dominated by a huge skylight. We all face Mr McKenna, who sits cross-legged on a black leather armchair, wearing a pair of baggy no-brand jeans and a T-shirt that says 'DMT'. This stands for dimethyltriptamine, the strongest and fastest-acting organic hallucinogen known to man (Mr McKenna will defend only DMT, psilocybin and marijuana - nothing man-made). His Birkenstock sandals are placed neatly nearby, and he wears black woollen socks.
A bearded academic type, Mr McKenna does not need fashion to prop up his arguments. His learning and powers of language slowly unwind and coil around us, until eventually we are mesmerised, our token resistance crushed by the irresistible force of his rationale. History and nature; the psychedelic experience; prohibition of same by religion and capitalism; human proclivity for 'altered states'; Oriental and Western philosophies; it is everything you have ever read and more.
Botany, biology, mathematics, quantum and Newtonian physics, chemistry - if you had trouble with it at school, he is sure to be au fait - all trip lightly off his tongue, along with classical quotations. This is the McKenna 'rap', the reason why people have paid pounds 30 a head to be here. 'Hallucinations are data about reality,' he says. 'They are as dependable and as 'true' as any other source.
'We have to recognise that the world is not something sculpted and finished, which we as perceivers walk through like patrons in a museum; the world is something we make through the act of perception.' He talks like a man reading out his own thoughts in essay form: at one point he actually says 'paragraph break'. Only he has no notes, no prompts.
Things move, gradually at first but accelerating all the time as his imagery resonates more powerfully. When he answers questions his words are vivid and his thinking clear and unhurried. He describes the Logos, where language is visible, a higher form of communication, a type of linguistic and spiritual evolution, and I'm damned if you are not getting a glimpse behind the dusty old drapes of 'meaning' and 'reality' even as he speaks.
And it looks very appealing, this alternative world he imagines for us, this higher form of consciousness to which we are all party but which we so rarely explore, largely because of our cultural taboos and farcical drug laws.
As we break for food and drink, I realise how fast his argument has proceeded and how far we have climbed, until we are right at the peak of this man's thinking, way up there, floating off and gliding over such dense concepts. And he has taken us all this way with not so much as a cigarette paper in sight. Forty people, soaring on one man's imagination, logic and humour. Two hours have passed like magic.
'But the point is not to listen to Terence McKenna,' he says. 'The point is to go home and get loaded.' You don't need telepathy to know that 40 people are thinking: that's my kinda guru.
After the break Mr McKenna resumes with his theories about our evolutionary path, involving a lengthy description of communication between octopuses. It is dark, and on the wall behind him our host Danny, who runs an audio-visual company called Project Love, is screening sub-aquatic imagery. 'Stronger doses, more often' is Mr McKenna's chilling, or if you prefer, exhilarating, advice.
You probably know what I found most disturbing about Mr McKenna's lecture - apart from his voice, nasal yet piercing, a laid-back call to reckoning. What bothers me is that, as a tax-paying professional, with Significant Other and five- year-old daughter, great friends, a good home and neighbours, I certainly do not think of myself as a radical. So I was worried because nearly everything he said made sense to me.
Somehow I knew he would dare me to act on my beliefs, and he did. Commitment, that is what he wanted. 'When are we going to come out of the closet?' he asked. And that is where I finally saw reason. I could get in a lot of trouble if people thought I took hallucinogenic drugs. Ha, the psychedelic experience] But he almost talked me into it. Phew, that was close.