In the summer of 2012 my friend Stuart offered me a ticket for a concert of Japanese music at London’s Barbican. The concert was scheduled for a Saturday afternoon the following February, nine months away. I was impressed by Stuart’s long-term planning skills, but I understood what was going on when I saw the line up: two musicians from Japan, one (Kumiko Shuto) playing the biwa.

The biwa is the crystal meth of the lute world – once you’ve seen it played, everything looks different. You need more. The biwa is pear-shaped, but in a good way. Four strings, hit hard, really hard, with an enormous plectrum that looks like it was just wrenched off a samurai’s war helmet. And sometimes caressed with a delicacy that tingles the shoulder blades. Anyhow, if someone is visiting with a biwa, Stuart and I drop everything and attend.

The main reason Ms Shuto and her colleague, shakuhachi player Kifu Mitsuhashi, were coming to the UK was to play Toru Takemitsu’s November Steps that evening with the BBC Symphony Orchestra, as part of a 'Total Immersion' day of Japanese music. Takemitsu’s piece had been a watershed for me. The day I heard a recording of it was the first time I ever heard the shakuhachi, a flute I became obsessed with in my early 20s and still play today. The prospect of hearing November Steps live was thrilling. But the afternoon concert would be just shakuhachi and biwa, close up and alone.

Time passed, and I heard a rumour that I might be invited to take part in an improvised piece involving both Japanese traditional and western instruments, at the Barbican. For a concert one afternoon in February. Dopily, I realised I already had a ticket to my own concert. Even more slowly did the BBC actually contact me about the event. The concert website continued to say Shuto and Mitsuhashi were the only artists performing, while I was eventually booked to play alongside an ensemble of British players. I called Stuart and explained he would be listening to me, rather than the Japanese visitors.

Incisively, Stuart phoned the Barbican and cancelled his tickets. No biwa, no deal. Now the afternoon concert would feature myself with the Okeanos ensemble, playing Japanese trad music, a suite by UK-based Japanese composer Dai Fujikura, and a “fusion-improvisation” mixing players from the BBC Symphony Orchestra with Japanese instruments. To prepare this ten-minute improv, nine hours of rehearsal were scheduled.

It’s sometimes said that classical players have trouble improvising. Well, these particular musicians were brilliant at it, and the ten-minute piece (with the help of a ‘map’ from Fujikura) came together quickly. Maybe nine hours rehearsal was over-generous, but I had a lovely time. Orchestral players know a secret that some improvisers don’t: you needn’t play all the time.

The mystery of the biwa and shakuhachi concert was partially resolved: Shuto and Mitsuhashi (both sporting beautifully sculpted quiffs) performed in a BBC studio two days earlier, recorded with a live audience. The studio strip lighting was brutal, but the playing magical. Shuto’s double-pronged plectrum tingled parts of my spine I didn’t know existed.

That afternoon our 10-minute improvised piece was a success – trust me, I was in it. By this time we were a tight-knit ensemble, bouncing sounds off each other with delight. Our title, “Hidden Tone”, arrived too late for the printed programme, which offered instead the gloomy prospect of “New Improvised Work”. But later that evening the concert audience also heard a great chunk of improvisation, without realising it. November Steps, for biwa, shakuhachi and orchestra, employs graphic notation for the two trad instruments. The work contains a nine minute cadenza, where the orchestra simply sit out, while the two soloists, digging deep into the vocabulary of their traditions, detonate improvised fireworks and surround them with silence. It’s a tremendous example of fruitful collaboration between composer and performing musicians, and to regard it simply as Takemitsu’s composition risks oversimplifying matters. But at least Takemitsu had the sense not to call it New Semi-Improvised Work.