Not only is his work still being exhibited - a new show opens at the October Gallery in London next month - but the sect he founded is still going strong. His strange brand of devil worship has even prompted his most famous disciple - the film-maker Kenneth Anger - to embark on his first original feature in 20 years.

Behind the sudden spurt of activity is an exotic underground world, in which Crowley, this would-be painter and poet who shaved his head bald, filed his incisors into what he called Serpent’s Teeth and told supporters that his excrement was sacred like the Dalai Lama’s, is the prophet of a new religion. Crowley called his creed Thelema, from the Greek word for "will". It was revealed to him by "preternatural intelligences" in 1904, and he transcribed their message into his sacred text The Book Of The Law.

The exhibition at the October Gallery is being organised by the Ordo Templi Orientis, the occult society of which Crowley was Grand Master and which now safeguards the Thelemite creed. "We’re not exactly a secret society, more a society with secrets," says his disciple John.

John and Sue, who asked not to be identified, live in Hastings near the site of the house where Crowley died, and they’re leading members of a mysterious international fraternity that has put them in touch with some unusual people. With Kenneth Anger, for example, the legendary film-maker and author whose collection of Crowley paintings I had come to their house to see.

This year Anger is making a film of the Gnostic Mass with a branch of the Ordo Templi Orientis in Austin, Texas. The title, he told me, has already ben misquoted by one American reporter as Nasty Mass. It will be his first film since Lucifer Rising in the 1970s, in which he and Marianne Faithfull performed rituals intended to make the Devil appear.

Anger has always been a fiercely independent director, making movies that resist the studio system, whose secret history he has told in his book Hollywood Babylon. Anger’s Magick Lantern Cycle of sensual, intensely personal movies beginning with the violent homoerotic fantasy, Fireworks, which he made in 1947 when he was 17, have been praised and emulated by directors from Jean Cocteau to Martin Scorsese. But wheras his early films used stars such as Marianne Faithfull and Anais Nin, he has now become more deeply involved than ever with the cult of Crowley, which he discovered as a teenager.

John and Sue carefully laid out Anger’s art collection on the floor in their lounge, casually mentioning that he’s coming to stay in Hastings after the opening of the Aleister Crowley exhibition.

"Crowley wrote the Gnostic Mass while touring Russia with a troupe of dancing girls a year after he became head of the British section of the order," John told me. "It’s a eucharistic ritual but it is not a parody of catholic ritual and it’s certainly not a Black Mass or Satanic Mass."

John and Sue insist that the Gnostic Mass is perfectly civilised, it’s a beautiful sensuous ceremony conducted before a seven-foot long altar. "We have a priestess who sits upon the altar and is a channel for the Goddess." Twenty-two candles are lit, and there is "a fire altar and and a water altar". A veil is drawn across two pillars. The priest begins the ritual in a tomb, which the priestess opens with a sword. She invests him with the cloak and crown, he takes her up to the altar and she does three-and-a-half circuits of it. "Each member of the congregation comes up, takes a cake of light, turns around and says, ‘There is no part of me that is not at one with the gods.’"

Crowley’s followers joke about his outrageous personality - you can’t expect the same standards of purity in a prophet as you would from a messiah, explains John - but they revere his teaching. "Do what thou wilt shall be the whole of the Law," said Crowley, inaugurating the only religion in which asceticism is sinful and excess the road to wisdom.

Whatever his flaws, they reject the myth of Crowley as an evil Satanist. "It used to be that the tabloids would dig Crowley up whenever there was a dull news day," Kenneth Anger says. "They made him into some kind of hob-goblin, but he was a wonderfully intelligent man, he had a sense of humour, and I find his ideas very interesting."

Yet of all the people anyone could take as a mentor, let alone a prophet, Aleister Crowley is one of the least plausible. Born in 1875 in Leamington Spa to a rich brewer who belonged to the Plymouth Brethren, he spent his life trying to become the opposite of everything he was expected to be. Instead of growing up a respectable Christian bourgeois, he became a pseudo-aristocratic sexual deviant with a reputation as England’s leading Satanist. As a child he ‘killed" a cat nine times to see if the superstition was true. After dropping out of Oxford and climbing mountains without any supplies except champagne, he joined a mystical sect called the Hermetic Order of The Golden Dawn, which boasted WB Yeats for a member.

He progressed to more transgressive forms of magic after deities "dictated to him" The Book Of The Law." He loved assuming false accents and spurious identities such as Count Vladimir Svareff, a Russian aristocrat in whose guise he toured Russia before the revolution. He pretended to be Irish and Scottish and supported Germany in the first world war. One of his books is called The Book Of Lies.

After the war, Crowley founded a Utopian community, The Abbey of Thelema, outside Cefalu in Sicily, and dedicated it to sex, magic and drug-taking. "It’s sort of the first commune," says Anger, who made a pilgrimage there in 1965 and spent a summer uncovering the murals Crowley had painted.

"He had a device painted on the floor which he called a magic circle," Anger told me. "He painted all these nightmarish murals on the walls that include a woman - a sort of grotesque hag - being copulated by a goat. He had a sense of humour which was very much his own."

The English press didn’t get the joke. Their accounts make Crowley’s experiment sound like something from Revelation. "He may well be described as the wickedest man in the world," raged the ultra-patriotic John Bull magazine in 1923. "We are impelled by the sheer horror and gravity of his recent devilries to make further exposures concerning what is going on at his Lust Temple..." The Sunday Express took up the attack. Anger insists that they wrote "totally fictitious rubbish like he was a cannibal and mentioning orgies - which might have been closer to the truth."

When one of his companions, a young boy from Oxford, died of gastroenteritis, rumours of Satanic murder were taken up by the press back home and Mussolini evicted the Thelemites form Sicily. Soon afterwards Crowley faked his suicde in Paris, then turned up for an exhibition of his paintings in Berlin. He spent the rest of his life wandering, paying the rent by making Elixir of Life pills with a secret ingredient - his own semen.

By the 1940s he was back in England, in Hastings, and claimed to have contributed to Hitler’s defeat in the Battle of Britain by positioning magicians along the south coast.

Looking at Aleister Crowley’s paintings, John and Sue - she’s an artist and John used to run a gallery - make no great claims for their aesthetic merit. It’s as an insight into Crowley, the man and his ideas, they say, that his paintings deserve to be seen. And something does shine through the Beast’s daubs. They display an intense, childlike determnation to live in dreams and fantasy. Aleister Crowley longed to be a poet and a painter, an artist-hero in the mode of Oscar Wilde, but he made himself into something much more 20th-century.

In creating an image of himself as a perverted practioner of black magic, he became the model for every cinematic Satanist villain from Boris Karloff in the 1930s film The Black Cat to Adrian Marcatto in Rosemary’s Baby.

At the same time he perceived how the same myth, inverted, could be a symbol of sexual liberation and social experiment. In the 1960s International Times called him "the unsung hero of the hippies" and The Beatles put him on the cover of Sergeant Pepper. Playwright Snoo Wilson advocates this view of Crowley in a film he’s working on about the Abbey of Thelema. "He’s a monster of egotism," says Wilson, "but I think his exploration of the psyche is quite fearless."

Crowley’s contemporary followers share the conviction that sex is sacred, that psychic experimentation is the road to happiness. These things are not different from the nightmare image conjured up by the Daily Express in the 1920s, they’re just understood differently. Aleister Crowley is an enduring figure of the 20th century because he captured, and made into a myth, the dissolution of universal moral codes. If you want prophecy, you need look no further than his slogan, "Do what thou wilt shall be the whole of the Law." This alone reveals him as the 20th century’s cut-price Nietzsche.