Peter Brook looks straight through you. As he holds out his hand to greet you, you can almost feel the actors whose hopes foundered as his pale blue eyes took the temperature of their souls. To see the great man, you must cross the stage of the former Paris musical hall Brook calls his mosque, and climb up a narrow, twisting staircase to a kind of platform where the most influential theatre director of the past 60 years spends his days, perched like a Himalayan holy man, a futon in the corner, above the railway lines of the Gare du Nord, scene of some of the most baleful comings and goings of the last century, from the trenches to the camps.
Just short of 85, the man before me, rubbing his large, expressive hands against the cold, has shrunk in his clothes. The Master is suddenly smaller, older, his nose bigger, his eyes more blue, his voice more nasal. In short, he is more like another of his many monikers, the King of the Trolls.
The day before I mounted the stairs at the Bouffes du Nord, now painstakingly restored to a chic shabbiness, I rang a young British playwright and a director to ask what they really thought of Brook now. "I still believe in God, but I don't feel the need to go to church any more," the writer said. "Look, he has best theatrical brain since Brecht, but he hasn't done anything decent for 20 years, not since The Mahabharata. I blame the French. He's gone mouldy like their cheese."
The director bemoaned how Brook had become as much a sacred cow as the "holy theatre" he once raged against. Everything he does is expected to be a milestone. "If Brook was to stand and fart for an hour on the stage of the National, you will have people queuing to tell you he is a genius. The myth has killed the man."
There is certainly a danger of forgetting what Brook has achieved. This is the man who, having made his name as a master of eye-popping spectacle, suddenly stripped stages bare and let audiences' imaginations do the work for them. In productions like Marat/Sade and The Ik, he pared theatre back to the human body itself; then, with Ted Hughes's Orghast, went one step further by dispensing with words altogether in the search for a universal language of grunts, cries and sighs. Always Brook seems to be searching for the shock of the simple, resurrecting the use of masks, mime and puppets from traditional ritual and performance, to show how little is needed to transport audiences. Yet his ideas, once so revolutionary, have now been so absorbed by the mainstream they have become obvious, even banal.
The Brook I find before me is somehow more himself, more reduced, more human, as if a balance has finally been found between the Monster and the Mystic. The octogenarian Brook is, if anything, more in a hurry than the fortysomething one who burned through the RSC, the West End and Broadway in a fever of invention, exhausting the possibilities of conventional theatre before disappearing literally into the desert with a band of actor-disciples including a young Helen Mirren, who got to dig the latrines.
Brook began to slip into exile in the late 1960s, shortly after writing The Empty Space, whose opening lines became the commandments on which modern theatre was built: "I can take any empty space and call it a bare stage. A man walks across this empty space, whilst someone else is watching him, and this is all that is needed for an act of theatre to be engaged."
For the next three years, he tested his theories and the limits of his troupe in every fly-blown African village they threw their carpet down in. He worked and reworked Orghast, as well as his own adaptation of the Persian epic The Conference of the Birds, travelling from the Sahara to the Niger Delta and then to India, Afghanistan and Iran, seemingly oblivious to the threats of dysentery and defection. The results of these experiments changed theatre for ever and made Brook the father of fringe.
'Violence is the ultimate laziness'
Yet only now is Brook finishing the play that was one of the drivers of that journey. Eleven and Twelve has been stewing away in his head for nearly 50 years. Played out on an almost bare, sand-strewn stage with a cast drawn from all corners of the earth, it is the essence of Brook: spare, deceptively simple, profound and magical, throwing open a trapdoor into a world where its audiences would never otherwise have tumbled. The work, which comes to London next month, is based on the memoir of an obscure Malian Muslim mystic, Tierno Bokar, a leader who put an end to a bloody religious war by conceding that his opponents were right. He would have passed unnoticed outside west Africa had not one of his disciples, the writer Amadou Hampâté Bâ, bumped into Brook in the 1950s.
On one level, this story of a dispute between sufis (who seek oneness with God and nature) over whether a prayer should be said 11 or 12 times is an allegory on fundamentalism. It also works as a critique of divide-and-rule colonialism, with Mali's French rulers turning one group against another as demands for independence mount before the second world war. But perhaps it is most powerful as a parable on the sacrifice that tolerance demands, as Bokar is eventually ostracised by his own people.
"To be violent is the ultimate laziness," Brook says. "War always seems a great effort, but it is the easy way. And false non-violence is also an idol." To him, the tolerance practised by the UN – with its muddy compromises and horse trading, born of "old-fashioned English liberalism" – is not tolerance. "It is not taking the bull by the horns and saying from the start: whatever our differences, nothing is going to be the cause of violence between our tribes. That is the most difficult choice of all, and it is one that Tierno makes, knowing, like Martin Luther King, that he will have to pay for it."
Brook has already taken one bite at the story of Bokar four years ago, but typically he wasn't satisfied (he reworked The Mahabharata for 20 years before letting go). The perfectionism and endless experimentation come from his scientist parents. In his memoir, Threads of Time, he tells how his father, a man with a quotation for every occasion, would return home to find his wife conducting experiments in the kitchen rather than cooking dinner. Brook senior, who invented the laxative that was to bear the family's name and secure its fortune, believed everything could be improved, and never left home without a pencil and paper to prove the point.
"As a young man, I experimented with everything," he says. Men, women, ideas, drugs. "LSD opened me to perceptions I did not know were there, though I only tried it once."
An epiphany with Salvador Dalí
Eleven and Twelve's themes of letting go and the need to pass on wisdom chime with a man in the middle of his ninth decade. "One tries to leave a living trace with people, in which they can reflect on what they are doing. The thing that I have a horror of is ideological theatre – Shakespeare never told us how to think. I have great respect for Brecht, but his path is not mine."
The play keys into another side of Brook that journalists and biographers have shied away from, either out of fear or embarrassment: his lifelong search for a spiritual path, beyond the success and celebrity that came so early and easily. There is more than a little of the sufi in Brook. And in Bokar, he has found a hero of Shakespearean scope who matches his own spiritual master, the Russian-Armenian mystic George Ivanovitch Gurdjieff, whose Meetings With Remarkable Men, a partly imagined account of his wanderings among the sufis of central Asia at the turn of the last century, Brook filmed in Afghanistan before the Russian invasion.
Gurdjieff's ideas on movement and proportion, strongly influenced by the dervishes he encountered in Istanbul in the dying days of the Ottoman empire, had a profound effect on the young Brook. "I couldn't believe that scientific thinking and religious thinking should be in opposition. There must be a link. When I saw that what we call beauty is not an aesthetic matter, but that there is an absolute law, the golden section, that relates to proportions and numbers, I knew at once it made sense." His first epiphany came while reading a book by the Romanian prince Matila Ghika while staying with Salvador Dalí in Spain. Classical art, it turned out, owed its harmony to its mathematical relationship to the human body. To a boy brought up on his father's maxims that everything becomes clear when reduced to numbers, this was powerful stuff.
Gurdjieff had died by the time Brook discovered him, but he still may have taught Brook a thing or two about being a guru. Artists don't so much work with him as join him on a journey. The sufi disciplines Gurdjieff adopted from the dervishes appear to have given a structure to Brook's restless, questing spirit – which saw its greatest flowering, up until now, in his sublime The Conference of the Birds. In it, the hoopoe bird leads all the birds of the earth towards their master. Only 30 last the course. Yet Brook is guarded, extraordinarily so, about Gurdjieff's influence. "This is something so rich that nothing would be more harmful than trying to encapsulate it in a few easy phrases." What would mysticism be, after all, without its mystery?
Yet it is to The Conference of the Birds, and an old sufi parable about butterflies and a candle, that Brook turns for the final image in Eleven and Twelve. All the butterflies wonder what the light on top of the candle is and what would happen if they entered it. The bravest throws himself into the flame and, as he disappears, the butterflies' master says: "This one has finally understood. And he is the only one who knows. And that is all."
Someone came to Brook the night I saw the play and told him that this meditation on the search for the truth and the price it demands could be taken as a justification for suicide bombing. Was the butterfly not blowing himself up for God? "I suppose," says Brook with heavy sarcasm, "this young person is rather pleased with himself, that he has discovered what all [Bokar's] talk of non-violence really hides – that it is to encourage suicide bombing?" For a fleeting second, there is anger in those cool, blue eyes.
For the past 70 years, Brook has been a butterfly throwing himself at a flame. His life, too, has been a search for answers to the big questions. But there will always be those who don't or won't get it. And, even at 84, you get the feeling that he will never quite understand why.
• Peter Brook will give the inaugural Peter Brook lecture at the Barbican Pit on 6 February 2010 at 4pm. He will be in conversation on 9 February 2010.
