I catch him on a quiet afternoon in Paris, between a recording session and a recital. As I'm early, he carries on practising for a while: a figure so naturally hunched that his body seems to have reshaped itself as an extension of the instrument. But he doesn't so much practise the Brahms Ballade in front of him, as meditate on it: intently studying a page, then turning back to the previous one, then forward, then back again, till I lose count. Then he plays a few slow bars, over and over again, varying the pedalling. No fireworks, no letting rip: an intense and private communion.
When he finally stops to talk, it's in German, the language with which, after Russian, he feels most at home. Home was - still is - St Petersburg, where he studied for 11 years at the conservatoire. The only child of music-loving parents, he wanted at three to become a conductor, and stood on a little podium waving a miniature baton - strange how many pianists start like this - while Beethoven and Mahler went round on the turntable. "One day they invited a piano teacher round, and asked what should be done with me. She said, `Nothing for the time being, but in a year's time I will teach him.' Then I forgot my dream of being a conductor."
He went on to win the Tchaikovsky Competition at 16. How many hours a day did he practise for that? "I don't remember. But I can tell you exactly how many I practise now: 24. Because, for me, the most important work doesn't happen at the piano at all: it's when something comes together in my head." Are there particular moments when he gets inspiration? "No. First you must internalise the music. The inspiration you leave to concerts, to the special state you are in." When the muse takes over? "Everything in art comes from above. All one's energy comes from the cosmos." No nerves then? "Nerves are an inextricable part of it all. When you play as if you were drinking a cup of tea, that's not music. If I don't feel anxious before a concert, I wonder what's wrong. It's precisely what's missing in the studio: I absolutely must feel it." He's friendly, but wary; each question is politely dealt with, and the conversational ball put back in my court.
Why were there tensions between him and his producer in the studio this morning? "Editing disturbs the balance of things. Without `corrections' my recordings are always better. For me the original is the model, and any change - even a single note - is a distortion. They haven't yet had the courage to put me out uncut. Next time they will." He says this with a determined glint.
He doesn't play chamber music: "For that, musicians must be permanently matched. If you merely meet up to practise a couple of days before a concert, no real music comes out of it." Does he teach? "I have one student at present." A good one? "Not particularly." (Let's hope he or she doesn't read this.) Who are his favourite pianists? "Horowitz, Rubinstein, Gilels, Gould, Solomon, Schnabel, Rachmaninov." All dead! "Not for me. When I speak of Gilels or Gould, I always speak in the present tense. Music for me has no time, no geography." And thus it is with composers. "It's not that the best music has already been written, but there won't be anything better, because music has no development. Each great composer brings a new world, which is completely self-sufficient."
His mechanical expertise, he insists, is a newspaper myth, but he does observe that the world has too few good pianos, and too few good technicians. He practises on stage before a concert, "to get to know the piano, and the acoustic". And concerts are his governing addiction: "If five days pass without a concert, I feel bad. It is not my normal condition." This condition was seriously upset by America's embargo on Russian performers during the Afghan war. "For eight years I could not play in the US." What about playing in Russia now? "I only play in Moscow, Nizhny Novgorod and St Petersburg. Nowhere else is safe, and there are problems with pianos, and power cuts." What does he want for Russia? "That there should be no more war, no more political extremes. Stability." Does he feel nostalgia for Soviet stability? "It was not stable. We were all Communism's victims. Stability is interwoven with human rights." He gives the bleakest of smiles.
As tennis matches go, this has been quite fruitful, but the initial sense of mystery remains. So I ask around a bit, and discover some interesting things.
The "practice" on which I eavesdropped was, if anything, busier than usual: whole hours can pass in contemplation, before he plays a note. And the studio tensions were the tip of an iceberg: his harassed producer Yolanta Skura - herself a former pianist - says it took her four years to persuade him to re-record four bars. "Last week he spent three days listening to all the possible places for making a single edit - and finally refused to make it. He has l'esprit de contradiction - every new idea gets a nyet."
For Sokolov, she says, a concert is a "sacred moment", to which every recording session should approximate. "For the first record I made with him - of Chopin's Preludes - he insisted on doing it in a theatre lit as though for a concert. He appeared in evening dress three days in a row, and in effect gave three entire concerts."
And he'll travel a thousand miles to find the right piano. The "newspaper myth" about him dismantling pianos is not a myth at all: when he encounters one he's not played before, he strips it down to its tiniest parts and notes their serial numbers; only after that will he play it. He has been known to tell Steinway-owners things they never knew about the history of their pianos: where they have been, which craftsmen worked on them.
Far from being hard on his students, he buys books for them abroad which they can't get at home, and he habitually goes back to St Petersburg laden with medicines for friends. His financial generosity to musicians in need - often dispensed by stealth through intermediaries - is something you learn about from his friends, but never from him. His agent despairs of getting him to discard the coat and scarf he has worn for the last 20 years.
With his wife - his main line of communication, after the piano, with the rest of the world -he is a connoisseur of painting, but he has other more surprising areas of expertise. One of his agent's duties is to keep him supplied with the latest flight-path manuals; he knows as much as pilots do about navigating big planes, and has on occasion proved to know more. He reads voraciously about space research - and no less eagerly about Nostradamus. One of his idler games is deciphering bar-codes. There's more intellectual energy here than music could ever soak up.
Those who work with him all testify to his endearing eccentricity: the conductor Trevor Pinnock recalls him warming up for a Beethoven recording by playing William Byrd. And he seems wonderfully consistent: the Russian conductor Anatoly Grindenko, who went to primary school with him, says he hasn't changed at all. "He was modest and quiet: he didn't rush about, any more than he does now. He wasn't a wunderkind - just a normal boy, with abnormal gifts, who knew what his goal was, right from the start.
He was always a noble musician."
But Grindenko also recalls something painful: when Sokolov won the Tchaikovsky competition, he was whistled and jeered by the audience. Grindenko puts this down to the Muscovites' preference, in 1966, for showy Americans. But it may not have helped that Sokolov is Jewish. Indeed, neither he nor his friends will discuss the way he was kept out in the cold by the Soviet authorities, and prevented from doing foreign tours. In the West, this was deduced from the mysterious series of cancellations which dogged his name throughout the Seventies; this is why he is now, at a relatively late age, still in the early stages of a new and burgeoning career.
"Until Communism fell," says Skura, "Grigory lived in fear. He always tried to keep his papers in order, but he was always afraid there would be a hitch. He was always pessimistic - and that pessimism has stayed with him." This sheds different light on his compulsion to perform - and even, perhaps, on his passion for flightn
Grigory Sokolov will play Bach and Chopin at St John's, Smith Square on Monday at 1.00pm (0171-222 1061). The concert will be broadcast live on Radio 3. Sokolov's CDs are released on the Opus 111 label; the latest is Schubert's Piano Sonatas D 894 and D 960