The second half of Cheltenham Music festival this year includes a mini-festival within the main programme. Devised by the violinist Katharine Gowers, Time Capsule 1914-1918 is a year-by-year showcase of the chamber and instrumental music of the first world war. In the year of his 150th anniversary, it's appropriate that Debussy features prominently, and the second concert, devoted to 1915, included two of his three late sonatas, those for flute, viola and harp, and for cello.

Gowers has assembled an impressive roster of soloists for the series; in the laconic flute, viola and harp work the fabulously supple playing of Emily Beynon, principal flute of the Royal Concertgebouw Orchestra, was the centre of attention. The contributions from Jennifer Stumm and Sally Pryce were wonderfully judged, too. Steven Isserlis was partnered by Connie Shih in the cello sonata. Between them Henning Kraggerud and Christian Ihle Hadland played Szymanowski's violin-and-piano Mythes with a great deal of technical finesse but without ever really suggesting that these quasi-modernist pieces are anything more than decorous note-spinning.

There was much more substance after the interval with the considerable bulk of Max Reger's Clarinet Quintet Op 146, in which the Escher Quartet were partnered by Matthew Hunt. The quintet is rarely encountered in concerts. Its mood is generally melancholy and autumnal – Brahms's late clarinet quintet is an obvious model, right down to having a set of variations as its finale. In the first movement especially, the music has a tendency to drift into the chromatic quicksand that had been Schoenberg's natural habitat a few years earlier. But it also possesses a quality not often associated with Reger, charm, and this performance, with fabulously refined playing from the Escher, and Hunt's clarinet seemingly incapable of making an ugly sound, did it full justice.

• Available on iPlayer until 18 July.