Peter Sheppard Skaerved & Guests, St John's, Smith Square, London

Benjamin Britten may have died as long ago as 1976, but his published output, particularly from his immensely productive earlier years, has just gone on growing and growing. It was no surprise at all to learn that, in trawling the Aldeburgh archives for his new Britten biography, the composer David Matthews had netted yet another substantial find in the form of Two Pieces for Violin, Viola and Piano dating from 1929, when Britten turned 16. Its belated world premiere made a fitting climax to this Britten recital presented by Haus Publishing in St John's, Smith Square, to launch the biography.

As an accomplished viola player, Britten evidently wrote the Two Pieces for himself and two schoolfriends, although Matthews could find no evidence that the three had ever managed to get through them. These are, indeed, remarkably sophisticated structures: a kind of vagrant, volatile valse triste, and an iridescently scudding scherzo and trio both in a highly "advanced" mode of chromaticism. As realised by violinist Peter Sheppard Skaerved, violist Dov Scheindlin and pianist Aaron Shorr, the extraordinary detail and fantasy of the instrumental writing already seems to tell of the young Britten's fascination with Schoenberg's Pierrot Lunaire.

But then, as we now know, Britten's mid-teens, when he was studying with Frank Bridge, were the most self- consciously modernist years of his creative life.

Scheindlin also offered a beautifully shaped account of the searching, at times agonised, so-called Elegy for solo viola that Britten composed the day after leaving school. And reverberations of his teenage boldness continued to sound through the more familiar idiom of his early published works: patches of tingling dissonance in the Holiday Diary piano suite Op 5, given a spirited, sensitive reading here by Britten's protégé Ronan Magill; and the splintered, virtuoso Suite for Violin and Piano Op 6 of which Skaerved and Shorr gave an edge-of-seat account to open the concert.

This conspectus of early Britten was neatly butressed by works by Bridge and Matthews himself. The latter's new Duet-Variations for Violin and Piano proved a substantial recomposition of his much earlier set for flute and piano; its opening pages sounding attractively enhanced in the new version, and with a seamlessly integrated mid-point cadenza devised by Skaerved and Shorr.

But the concert's other revelation was Frank Bridge's Trio: Rhapsody for Two Violins and Viola, dating from the same year as Britten's Two Pieces. This proved a continuous 15-minute flight of airborne atmospherics, occasionally running into patches of more passionate turbulence but carried off with exquisite point and finesse. Astonishing that music of such dazzling professionalism and subtle individuality should still remain so little known.