It was this work that led Leary to Harvard in 1960 and experiments with psilocybin (the ‘active’ ingredient of ‘magic’ mushrooms) and later the then still legal LSD. Leary’s investigations unwittingly paralleled experiments by the CIA in a similar field but with a less altruistic intent.

Harvard was soon to be 'seething with drug consciousness' and Leary, by the middle of the decade, a notorious figure and author of the famous phrase 'turn on, tune in, drop out'. This he later ameded, taking into the account the size and strength of the younger generation, to 'turn on, tune in, take over'.

Imprisoned for the possession of a modest half-ounce of marijuana, the man escaped to Europe but was eventually 'informally extradited' back the US to complete his sentence.

Now 63, Leary is, ironically perhaps, among the most highly-paid performers on the lecture circuit. The debates on politics and morality between himself and G Gordon Liddy (ex-lawyer, ex-FBI special agent, man behind the Watergate break-in) provides the basis for Return Engagement, a film by Alan Rudolph chronicling eight days in the lives of the pair. Meanwhile, Leary’s autobiography, Flashbacks, is published next month.

To tie-in with both film release and book publication, Leary was due in London this week. Alas, he was denied entry to the UK on ground of being 'a threat to public order'.

"I plead guilty to that!", asserts the gobbler of some 5000 LSD doses when I finally make verbal contact over a remarkably clear phone link (I can’t but wonder who else might be listening) to his Hollywood home.

Far from being the burned-out drug casualty that many assume, Leary in conversation is lucid, enthusiastic and sprightly of wit. He continues:

"I do aim to stir up disrespect for that kind of police state bureaucracy. I continually argue for the rights of the individual over the power of the state. The British government are, therefore, presumably showing themselves to be afraid of these rights."

In Return Engagement, Leary finishes up almost seeming to have something in common with the ostensibly right-wing Liddy: a couple of oddballs turning their pasts into money, enjoying the publicity and showbiz razzamatazz. The basic ideological differences don’t stand in the way of entertainment, leaving the two as slightly clown-like figures.

"The editing shallowed out the very profound differences. Liddy looks to the past while I’m very much looking to the future and the evolution of intelligence."

In the film, you’re seen grinning at youths in an amusement arcade and expounding the virtues of video games.

"My interest is not with video games per se but with the use of video educationally. For example, I’ve always held that it’s much better to teach five to ten year olds chemistry using screens that can show electrons darting about rather than just having a description of that on paper.

"There are many different levels of intelligence but it is really about understanding the equipment that you have and the outside reality, so that you can harmonise and fuse the two to increase knowledge. The key is to evolve, change and develop an understanding of evolution."

And there’s a lot of resistance to this..?

"Yes. I stand for change (in Flashbacks, Leary describes himself as 'a genetically determined change agent'. Aldous Huxley told him: 'Be a cheerleader for evolution') and bureaucracies of both left and right are very much opposed to that."

During the public question and answer section of Return Engagement, there is a Vietnam veteran with plastic eyes and two hundred pellets lodges in his skull. He cites: ‘followers of Timothy Leary’ as being responsible, they took LSD, hallucinated and began firing their guns... it’s the only part of the film where Leary seems lost for words.

"That man just made a very basic appeal to the emotions. It was not possible for me to have rational discourse with him. I felt very sad for him and there was no way that I could act as a smart-arse.

"I felt great deal of compassion for him, he was probably mentally disturbed but he was very good example of a civilisation that operates on very primitive emotions of good versus evil. What actually caused the harm to him was guns and not drugs, and I very much favour strong control of guns. Liddy, meanwhile, was arguing the opposite.

Do you still take drugs?

"Yes."

LSD?

"On special occasions. Weddings, birthdays, etc."

What's your view of Britain?

"There are pressing problems and lack of confidence. Britain is in great danger of returning to the police state that it used to be. As evidenced by the Falklands and, of course, not letting me in. Britain should invest in computer projects: artificial intelligence or the Knowledge Industry as it has become known."

What are your views on the shooting down of the South Korean airliner?

"I’m probably the greatest enemy of the Soviet Union and the monstrous gangster bureaucracy they have there. But I’m ashamed as a patriotic American that there has been no denial from the US government that surveillance equipment is used aboard civil aircraft.

"I’ve found Reagan’s reaction disgracefully provocative. He’s been instrumental in the development of a war-like situation, he’s exploited the incident for his own ends. The Cold War is heating up and Reagan is responsible."

Finally, whatever happened to the LSD movie that Cary Grant was getting excited about in 1962 (documented in Flashbacks)?

"Ha ha," giggles the Doctor, "it’s still waiting to be made."