There is some sort of orgy going on in the ICA's Nash room. Members of the public, pistachio-munching and Merlot-swilling, are crowding in, drawn by the marching beat of the snare drum and crescendoing zombie vocals emanating from TV screens at the back.
On the left monitor, a man swaddled in white is being carried to the foot, or rather head, of an eviscerated and crucified lamb. On the right, a table is being prepared for a Dionysian feast: grapes, tomatoes and fish are rent apart and brilliant paint is poured on; and, in the centre, someone posing as St Sebastian has entrails strapped to his side with bandages, which are then poked about while more body fluids, blood and wine are poured on. This stuff makes Damien Hirst look positively boil- in-the-bag.
A little man in black with a long beard is darting about, co-ordinating this extraordinary mass, which he calls "The Orgies Mysteries Theatre". He is Hermann Nitsch, the artist whose "action painting" was considered so dangerous by the city of Vienna in the Sixties that he was thrown into prison several times for crimes of indecency. He is now, of course, a national treasure.
The return of one of the art world's most extreme extremists to London (the last time he visited, in 1966, his performance outside the ICA was broken up by the police and the curators were prosecuted) has brought together Nitsch aficionados from all over to hear him talk: some dedicated followers of his creed, others just heard a rumour that some guy had planned his own crucifixion and came along out of curiosity.
When Nitsch first preached his doctrine of "abreaction" (the unblocking of repressed energies) through the theatre of cruelty in 1962, most people's experience of violence and sensual gratification was limited to Westerns and Mills and Boon.
"I take upon myself the apparently negative, unsavoury, perverse, obscene, the passion and the hysteria of the sacrifice so that you are spared the sullying, shaming and descent into the extreme," he declared, Baptist- like. (More recent manifestos have taken on a Christ/Kurtz-like dimension: "I AM THE PAINTER who SLAUGHTERS and HUNTS the ANIMAL FOR YOU".) The same year he made the headlines with fellow Vienna Actionists Otto Muhl and Gunter Brus when all three walled themselves up in a cellar for three days with alcohol, sculpture materials and a crucified lamb.
The time is right to unleash Nitsch again. The now world-famous artist has chosen an "underground" gallery in London's Old Street for the retrospective. It is 35 years after the ICA's fated "Destruction in the Arts" show and the institute is hosting a new "Violence and the Arts" conference this month (note "violence" and "arts" now go hand in hand). The question is, have attitudes to censorship changed that much?
Could it be that larger art establishments are still frightened off by the inflammatory content (entrails, mutilated genitalia, urine, aborted foetuses) of Nitsch's work? Previous contracts - one from the National Gallery of Scotland, another to mount a production of Massenet's Herodiade (a version of the Salome story) at the Royal Opera House - have been pulled due to last-minute panics.
Nitsch believes his work is "misunderstood" in 1997 more than ever. Modern- day activists regard him as a butcher and a sadist and yet, he insists, he "luffs" animals. He is poised on a wooden chair at the Underwood Street gallery with a flowing grey beard, his belly rising and falling heavily in his morning suit after an afternoon nap, looking more like Van Gogh's postman than the scourge of the Daily Mail reader.
Endearingly, even, he lists the animals at his farm in Prinzendorf, Austria: "two dankey, cows, sheeps, peacock, geese..." He stresses that 90 per cent of the animals he uses are slaughtered at their natural age and humanely. He rails at the meat factories ("very bad places") where animals are deprived of light.
Nitsch is pro-life in the pagan sense. "What I do is create a great feast. A feast of life," he says boisterously. "I believe an artist is like a priest. That's why I wear black. I am always full of jokes, I like to eat, drink and luff. Living a life of the moment - that's my religion." A 20th-century Dionysus? "Ja!! Except Dionysus is more than a god. It's a... structure, philosophy."
He describes a moment of Eucharistic "mysticism" when he puts his hands deep into the cavity of the slaughtered animal (a metaphor for setting free the animal in man). "It's the same as when I listen to Bach, Bruckner or Beethoven... as King Oedipus when he comes, his eyes streaming, screaming and crying - then he is a man like Jesus Christ. Then I have the feeling of the whole world, stars, planets and suns. Art can do this."
Nitsch was brought up in the small Catholic village of Prinzendorf and had an early interest in religion, later poetry. He suffered during the war: when he was six, Vienna was bombed by the "enemy" and the middle- class life he knew was utterly destroyed. An English curator, in the dock on charges of indecency, was later to defend Nitsch's work as an attempt to expiate Nazi guilt.
Since the war, Nitsch, a staunch pacifist, has waged his own war against politicians and everything "mediocre, lukewarm and cosy" about modern life. "I want people to wake up to their subconscious," he says. "Most are dreaming." The inscription on his pounds 300 book The Fall of Jerusalem reads "In times without wars, it's necessary to create them in tragedies".
Just as the central paradox of Nitsch's work is the celebration of life through the pathological performance, so the tumescent irony of his artistic life is that he has often been mistaken for a sort of S&M black pope (after the style of Anton Szandor La Vey) rather than the leader of fertility rites (in the style of Father Christmas) he would truly appear to be.
His work is saturated with the philosophy of Nietzsche, Jung, Freud, Eastern mysticism, positivism and cosmic philosophy. "Luff" is his ultimate goal, he says, and "understanding the broad spectrum of `luff' - joy to tragedy and Heaven and Hell". He counts among his fans several Catholic priests who are only too happy to exhibit his less messy Crucifixions above their altars.
Nitsch is no advocate of cinematic violence. "The way they kill on television is a nonsense. It is pretty and clean - you can eat and drink to it," he says. It lacks catharsis. "In my work you smell the entrails and blood and wine. I have never known people to become aggressive after my shows."
Nitsch is planning to perform his famous six-day "action" next summer. It promises to do for blood what Glastonbury did for mud last year. He thinks a society that "represses aggression" needs his macabre theatre more than ever. Paedophilia, necrophilia are all acceptable territory. "It is necessary that the artist speaks very, very loudly about these things. Science and art should show everything. Everything." It is not a question of morality.
Nitsch has not yet realised his dream of practising his art on human cadavers (in this, his followers are more radical - one boasted after the ICA talk that he had used real corpses). Nor would he ever consider taking a human life: "Looking at war photography is where my voyeurism ends," he says.
As for the rumours about his own crucifixion, Nitsch laughs so much he has to have a glass of water. "If I hurt so much as a little bit, I would give up the art straight away. In this, I think, the journalists are more radical than the artist!" he jokes. He has, however, generously volunteered his body "for young British artists" after his death.
Hermann Nitsch's work is on show at 30 Underwood Street, London N1 to February 1998.