Words such as jazz" and "contemporary" have become even less precise than "ambient" and "electronic". Over a few hours on the Sunday of the Clerical Medical Jazz Weekend in Bath you could have heard the expressionist cinema-inspired music of Max Nag, the fine modern mainstream of Denys Baptiste (with singer Julie Dexter) and the disciplined chaos of the 15-piece Brian Irvine Ensemble. When festival jazz programmer Nod Knowles had to fill out his introduction for a few minutes, he noted that Irvine's Belfast band (making their mainland debut) could have easily appeared in the following weekend's contemporary music bash, parts of which - the Shouting Fence, for example, or Joanna MacGregor's Gamelan project - could comfortably have been put into the jazz slot. What Knowles implied, in an unscripted, enthusiastic outburst, is that in the uncharted hinterland behind and beyond labels like jazz, contemporary and world music lie some of the most interesting musics of the present day.

Brian Irvine's body of work is a good example of the musical treasures half hidden in the cracks between the categories. He is one of those youngish composer/musicians who has been beavering away for a while –not in complete obscurity, but certainly off the beaten track that includes broadcasts, flash metropolitan commissions and discussions on the South Bank Show. He looks too much like a wilder version of Graham Norton to be taken seriously as a rock musician or a round artist. His conducting style with its gurning, torso-twisting, knee trembling and ill-fitting trousers- is so uncool as to be utterly cool. like composers Martin Read (Winchester) and Charlie Barber (Cardiff), Irvine has established a musical base far from london's fidgety hothouse, a nursery for composition with a regular group of musicians and enough financial support (teaching work, the odd commission and bits from local arts bodies) to get on with the business of making smart music in a culture that often over-rewards the dumb and/or the well connected.

Irvine's compositional style is dense and complex in a good-humoured and rhythmic manner. It has some of the hyperactive sound you might associate with John Zorn, Fank Zappa or Django Bates, delighting in his ensemble's practised ability to switch moods, tempi and sound levels at the flick of an elbow-sometimes guided by the cue cards that Irvine brandishes. In the six-part suite Bersudsky's Machines, which I heard at the Bath Pavilion last month, saxophonist Paul Dunmall adds some expert free-jazz fury to the precisely notated turmoil of the scores.

Irvine's scores use the interlocking compositional methods of jazz-funk as a metaphor for the Jean Tinguely like mechanical sculptures of Eduard Bersudsky (on display at the Sharmanka Gallery in Glasgow). You could compare the work to Conlon Nancarrow's piano workouts, or Mike Westbrook or the Jazz Composers' Orchestra, but Zappa springs to mind because the late Mother is contemporary musics crowd-pulling composer of choice: throughout Europe, music graduates grapple with Ensemble Modern-style versions of G-Spot tornado and Jazz From Hell. (Irvine also favours jokey titles such as Big Fat Pants and Stomach Remover.) Zappa's work is precise and structured enough to be read at sight by classically trained musicians seeking to goose up an evening of 2Oth-century America. But Zappa developed his music for a regular team of like- minded players who could memorise the notes, improvise and change gear at the merest gesture. Irvine's band is thankfully much closer to this rock/big-band tradition than his straight music peers.

Irvine is working in what I tend to call "creative music" rather than modern jazz or contemporary serious music. I'm using the term "creative" to distinguish it from "repertory" rather than "non-creative" - you only have to hear Margaret Leng Tan or even Harry Connick Jr in action to hear a great deal of creativity applied to the music of the past - but the creative music that is being made now is often straight out of the lab, the beta-version software waiting for friendly feedback. So an informed, curious audience is part of the process, and it was exhilarating to witness the reaction of Irvine's Bath Festival listeners, who banged the tables to demand an encore.