Daniel Barenboim is on the phone, apologising profusely. Somewhat improbably, he tells me he's just popped down the road to buy a jumper, having arrived in London in the expectation of a heatwave only to find himself shivering this morning. That a man as unfeasibly busy as Barenboim has time to buy his own sweaters – let alone make his own phone calls – is unexpected. But five minutes later, the polyglot, polymath musician strides into the lobby at Claridge's, bearing an Emporio Armani bag and that famously disarming smile – a smile whose persuasive power has convinced thousands of orchestral musicians, hundreds of Arabs and Israelis, numerous global politicians, even me – to do things they might never have imagined possible.
The pianist, conductor, author and lecturer turns 70 next year and still operates on a schedule that would give many 17-year-olds pause. Before this year is out, Barenboim will release his third disc of 2011; play a complete Beethoven piano concerto cycle in Israel; give 60 more concerts, including a tour with the West-Eastern Divan, the Arab-Israeli youth orchestra he co-founded in 1999 with the late Edward Said; and perform in 12 countries, as well as the West Bank and the demilitarised zone between North and South Korea.
Upstairs in his suite at Claridge's, a grand piano bears well-thumbed copies of Liszt's two piano concertos, which he would perform that evening at the Royal Festival Hall. I take this as gratifying evidence that a man whose musical achievements so often appear superhuman does, occasionally, have to practise. Pulling on his new jumper, he offers me a glass of "beautiful" red wine, though it is barely past midday; I thank him, but decline. And then suddenly, as is the Barenboim way, the smile has faded and he is talking very seriously about Gaza.
"One has to keep these pieces of information in mind," he tells me in his distinctive accent, a mixture of his Argentine-Israeli childhood and the English, Russian, German, French and Spanish he uses almost interchangeably. "One, that 85 per cent of the population of Gaza is under 30 years old. Two, that 50 per cent is under 16. And that these young people are the future for all of us."
Barenboim, a Jew who holds both Israeli and Palestinian passports, has recently returned from Gaza. In May, after various thwarted attempts, he finally made it across the border to perform a concert. Assisted by the United Nations and the new Egyptian government, which opened the airport specially for the occasion, he says he found the whole experience "deeply moving. One young man came up to me afterwards and said, 'When the international community ignore us except to give us food, it makes us feel like animals. When you come here and give us a concert, it makes us feel like human beings.'"
Not that Barenboim allowed the emotion of the moment to overwhelm him. "I told the audience afterwards that I believe very much in the justice of the Palestinian cause," he recollects. "But I also said, 'please allow me to tell you that I don't think you should try to achieve it with violence.'" The phone rings; Barenboim ignores it. "This is about the future of Palestine, the future of Israel, the future of the Middle East, and therefore the future of Europe," he says. "It is no exaggeration to say this. To think anything else is very short-sighted."
The last time I saw Daniel Barenboim was a little more than six months ago, when Mohamed Bouazizi was still just a fruit-seller in the Tunisian city of Sidi Bouzid; when places such as Tahrir Square, Misurata and Benghazi were still unfamiliar to most of us; and when a nuclear plant named Fukushima-Daiichi was still generating away in Japan. To say that the world has changed is an understatement. Nevertheless, most musicians might have been content to give a concert in aid of the Japanese earthquake victims. They almost certainly would not be drawing intellectual parallels between these events and the "sonorous air" that is music – nor pondering how best to live in this changed world.
But Barenboim is not most musicians. "I think it's imperative that every one of us rethinks everything we have believed in and understood until now," he urges. "These events – the Arab uprising, which we must really salute, and the Japanese nuclear catastrophe, which shows us the peril the world is in and how we only ever look at our own short-term interests – have exposed a total lack of strategic thought."