Hidden masterpiece

In fact, the concerto hadn't been played anywhere, by anyone, until 2004, when Leon Fleischer, Simon Rattle and the Berlin Phil gave the world premiere.

It was greeted as a flying success – a fine example of sharp-edged early modernism, as well-crafted, technically gratifying and inventive as other 1920 Hindemith scores.

The reason for the eight-decade delay had nothing to do with the quality of the score, but was down to one man – the very man for whom it was written in the first place.

Paul Wittgenstein was the pianist son of a wealthy Austrian industrialist and younger brother of philosopher Ludwig. When his right arm was amputated in a Russian field hospital during the First World War, he resolved to continue his career as a concert pianist and commissioned some of the most eminent composers of the day to write concertos for the left hand alone.

Thanks to his family's wealth and social connections, the Wittgenstein commissions amount to one of the most singularly impressive legacies ever accrued by a soloist.

Ravel's is probably the best known of the bunch; others include left-handers by Prokofiev, Strauss, Britten and Korngold.

But Wittgenstein was seemingly a tricky man to please. He told Korngold his piano part would have been unplayable if he had four hands to deploy. He told Prokofiev if he'd wanted a solo piece (as opposed to a concerto) he would have asked for one. He said Ravel over-orchestrated his score (possibly true).

And he disliked Hindemith's concerto so much he neither played it nor allowed anyone else to, and prevented it from being published during his lifetime. The score was discovered among his belongings when his wife died in 2002.

"It's not simple to describe the legacy left by Paul Wittgenstein," says Mustonen. "We're very grateful for the works that were written because of him. But because he didn't like some of the works they were denied to everyone else.

"You'd think that a musician dealing with composers the calibre of Prokofiev or Hindemith would see that these pieces might have value to others, even if they weren't to his personal tastes."

Why Wittgenstein disliked the score quite so much we don't know. But his subsequent behaviour raises interesting questions over musical ownership: just because he paid for the commission, should he have absolute rights over the notes? And what did Hindemith think of the fact that Wittgenstein wouldn't let anyone near the score?

"I would guess," says Mustonen, "that Hindemith, being a pragmatist, and also a very busy composer, simply got on with his next job. He probably didn't want and couldn't afford a legal battle. The most important thing is that now the piece is published and nobody can take it away from us."

What's it like for a two-handed pianist to play with one hand only? Mustonen describes some of the inadvertent pluses: "There's a technical benefit, which is us right-handed pianists need to strengthen our weaker hand. But there's a musical reason why left-handed pieces actually work quite well.

"Think about the placement of the hands on the keyboard. The strongest fingers – the thumb and fore-finger – are at the lower end of the right hand, but they're at the upper end of the left hand. That makes the left hand better for picking out a melody while using the weaker fingers to play the accompaniment."

"Performing with just the left hand can have a weird effect. You start to feel as though you only have one hand that's positioned in the centre rather than the left side of the body. All of your energy from both hands is channelled into the left hand, and the right hand almost fades away.

"Because of that I make sure to check in with my right hand now and again. 'Hello, guys', I'll say to my fingers, and I'll give them a little wiggle." Look out for that wiggle at City Halls tomorrow afternoon.

Mustonen is talking to me from his house in Finland, bellowing down the phone with cheerful bravura. He describes his surroundings: a snowy forest, a frozen lake, a wooden sauna by the side of the lake.

"I live about 45 minutes north of Helsinki," he says. "Here the most important sounds are wind, rain, insects and birds. Spending time here makes a nice contrast with my work, which happens in urban environments." He spends roughly half of his time at home in the forest, half on the road as a pianist, conductor and composer.

Over the next two weeks he takes up residency with the BBC SSO, playing all three piano concertos by Bela Bartok, a composer whose music he describes as "close to me since childhood", as well as the 'new' left-hand concerto. "The Hindemith score is very energetic, very exciting, with an almost Neanderthal power to it," he says.

"The middle movement is gentle and chamber-music-like. Pairing it with Bartok's third piano concerto makes a lot of sense. They were composers who had great respect for each other, and Bartok's first and second piano concertos are closer to the modernist style of this early Hindemith. But his final work, the third piano concerto, is a nostalgic look at his childhood in Hungary that Bartok wrote when he was unhappily exiled in the US. It's full of fond musical references, full of heartbreak and homesickness."

When I ask how Mustonen divides his own energies between composing, conducting and playing the piano, he uses Hindemith as a model.

"Hindemith summed it up when he described himself as 'a musician who composes, a musician who conducts, a musician who plays the viola'. I like this idea of the musician.

"There's an obsession with specialising that is actually a relatively recent phenomenon." He's referring to the fact that many composers these days don't perform, and many modern performers wouldn't dream of composing.

"Composers who don't interact with performers are like scientists in a lab," he says. So what does that make a composer who not only interacts with performers, but is one himself? "A musician. For some time I was reluctant to write for piano – maybe it lacked the mystery of other instruments. But I know a little bit about piano playing, so I suppose that helps."

Olli Mustonen plays Hindemith and Bartok with the BBC SSO at City Halls, Glasgow, tomorrow afternoon. The series continues on December 10 and 13.