Schubert Ensemble, Purcell Room, London

Just turned 50, John Woolrich has emerged over the past two decades not only as a vastly prolific composer, a resourceful teacher and an influential animateur of ensembles, festivals and whatnot, but a musician with an aesthetic all his own. While he is perfectly capable of constructing works on the broadest scale - witness his craggy Oboe Concerto of 1996 - much of his most characteristic work has emerged in the form of lapidary, often enigmatic miniatures; and, as a concert-planner, he has recurrently sought out comparable music by other composers.

This birthday programme given in the Purcell Room by The Schubert Ensemble proved typical in assembling tantalising fragments as much as "whole" works and in exploring the ambiguous gradations between original composition, transcription, arrangement and re-composition. Each half began with a recherché sheaf of virtually unknown fragments for keyboard alone, precisely characterised by the Ensemble's pianist William Howard.

Three opening chippings from Janacek's last year included his affecting little farewell to the lady-love of his old age, Cekam Te! (I am waiting for you!) jotted down on the same page as his actual Will. The second group began with an unused theme Wagner intended for Tristan, an incomplete, oddly schematic minuet by Mozart, a turbid shard of just pre-12 tone Schoenberg and a Schumann album leaf Rebus sounding like a forgotten movement of Scenes from Childhood.

As if in mordant comment on his own advancing years, Woolrich had also chosen to include three more substantial pieces by very young composers. From Schubert's 19th year, we heard the bucolic opening allegro from his incomplete String Trio in B flat warmly projected by the violin of Simon Blendis, viola of Douglas Paterson and cello of Jane Salmon. In the second half, William Howard joined them to welter through the surviving movement of the Piano Quartet in A minor by the 16-year old Mahler - already full of his characteristic Weltschmerz, if not, as yet, of his mitigating irony. It was left to a cosy little tea-shop-style Standchen by the 15-year-old Richard Strauss to supply that by default.

At the focal point of the aural soundscape, we heard three recent chamber pieces of Woolrich's own. In A Presence of Departed Acts (2002) for the guest clarinet of Duncan Prescott, violin, cello and piano, chiming piano-chord refrains alternated with gritty folkloristic episodes. In Sestina (1997) starkly convolved "shadows" of Debussy, Schubert and Beethoven ultimately resolved in resonances of Monteverdi.

And, by way of finale, sombre Woolrich arrangements of five valedictory Bach chorales preceded their transformation into the jagged rhetoric and keening lines of A Shadowed Lesson (2000) for the whole Schubert Ensemble, including the double bass of Peter Buckoke. If this seemed a baleful culmination it must be said that, as he acknowledged his audience, the composer looked happy enough.