Yet that's how the piano concerto that Joanna MacGregor will premiere in Liverpool next week has gestated over the past six years. "I put a piece of string from one side of my room to the other," says Bates with characteristic diffidence. "And every thought to do with it, I put on a scrap of paper, and hung it on the line. I chose a title which gave me carte blanche to go anywhere - What It's Like To Be Alive - and just let the thing unfold. It's been like walking along a river, seeing where it went."
The judges who awarded him the International Jazzpar Prize in Copenhagen last month praised the "kaleidoscopic and unpredictable" nature of his work, which they approvingly situated on the "brink of chaos". And if you listen casually to either of the CDs he has on the market, you'll instantly see why. Winter Truce is pervaded by the fuggy exhilaration of early Sixties "free jazz", and Here is the News bungs in everything from farmyard sounds to funk to neo-Bartok. Yet you soon become aware that there is a mind in control: shaping intricate patterns and textures, creating long passages of sustained lyrical thought, taking the sound down to a tiny point of light, then letting it blaze up in a wild conflagration. This is a very fruitful kind of chaos, over which Bates himself presides - sometimes at the keyboard, sometimes on the horn.
Bates was first picked up by the spotlights with his creation in 1983 of the Loose Tubes ensemble, which let some much-needed fresh air into the contemporary jazz scene. He had grown up in a home pervaded by music that was, as he puts it, "very loose, and full of accidents". And he had lasted just two weeks as a composition student at the Royal College of Music, where the pianos all bore notices forbidding their use for non- classical purposes.
Charlie Parker was his great hero, but Keith Jarrett was another, for being what Bates calls "a bridger". And bridging the jazz-classical divide is what Bates - and this new concerto - is all about.
But he doesn't want to abolish that divide: the two musics have different strengths. "Joanna practises eight hours a day - that's her life. Jazz pianists may go through a phase of practising that much, but after that phase their work lies in responding to other people, rather than endlessly honing their technique. I couldn't play the concerto I've just written."
Even MacGregor - the queen of crossover - will be taxed by it. "The writing reminds me of Charles Ives - a lot of big, heavy chords, and plenty of counterpoint. There's a marvellous piss-take of ragtime in it, very like one of Django's own improvisations, with all the semblance of honky-tonk but completely out of kilter. And a gorgeous middle section which he doesn't want to call a cadenza, but which is in effect one. The mood is like Satie - witty on the surface, but very dark underneath."
Bates is still happy to wear the jazz label, but he's leery of getting sucked into the trainspotting side of the scene. "Most people are conservative, and jazz audiences are no exception. There's a lot of snobbery about recognising standards: people feel comfortable when they think they know what's going on. That's why I've avoided them - I prefer to upset people, keep them on the edge of their seats. I want to keep adding new possibilities."
Earlier this year he composed a percussion piece for Evelyn Glennie in which every instrument was a kitchen utensil. But what struck Glennie, when she saw the score, was its apparent conventionality: even the saucepan parts sat sedately on the stave. "Why not?" he counters. "I've never felt the only way to communicate a new idea was to present it in a new style on paper." And he likes to give his performers their heads: his most detailed scores have passages of improvisation, moments of what he calls "vaguery".
He has two bands - a quartet called Human Chain, and a larger ensemble called Delightful Precipice - whose members are in some cases leaders of other bands. So the gospel according to Django is spreading fast. It will be seen in a Channel 4 film early next year - One In a Million - and he is currently casting about for a director to film Travel Cartoons for the Blind, four saxophone miniatures he composed for his two young children. His wife, the singer Beverley Hills, figures as newsreader in his most viscerally political track to date.
Meanwhile, he and MacGregor are hoping that one performance in Liverpool won't be the end of the Concerto story. As he puts it, with deceptive mildness: "I get very frustrated with projects which take me and other people a long time, and then just happen once." You listening, Collins and Decca?
Joanna MacGregor plays Django Bates's Piano Concerto at Liverpool's Philharmonic Hall on 8 Nov (0151-709 3789); `Good Evening... Here Is the News' is on Argo 452 099-2Reuse content