Medici String Quartet, St Andrew-by-the-Wardrobe. Chamber Domaine, St Andrew Holborn, London

One of the delights of the City of London Festival has always been the opportunities it gives for visiting attractive city venues that are rarely open to the general public. This year's Angel Series, introduced in an earlier review, toured 12 Wren churches; some extensively renovated, at least one larger one a little problematic acoustically. Yet all those I entered proved to be conducive spaces for listening to music.

The Angel Series offered art and poetry too. At every concert, one of the angel paintings by the talented Croatian artist Dragan Andjelic was displayed. These 12 imposing wooden icons, originally made for the Norfolk and Norwich Festival, have also been on view collectively – together with illustrations in progress for 12 telling poems specially written for the series by Gwyneth Lewis – at St Edmund, King and Martyr, where Andjelic has also been busy with workshops. Lewis's poetry was read aloud at some of the recitals.

As for the music itself, Chamber Domaine's performances of quartets by Beethoven and Shostakovich lacked much penetration and were further blunted by the size of St Andrew Holborn. Judith Bingham's My Father's Arms – new settings of three poems by Martin Shaw on "the dark side of childhood" for soprano (Helen Meyerhoff, offering a nice, pure tone but poor diction) and string trio – was uncharacteristically leaden and derivative.

By contrast, the Medici Quartet's recital, in the smart, woodily renovated space of the evocatively named St Andrew-by-the-Wardrobe, combined the London premiere of Nigel Osborne's Medicinal Songs and Dances and Shostakovich's Fifteenth Quartet with almost perfect results. It's good to see Osborne, a rare, idiosyncratic and provocative talent, back on the music scene again, though the social commitment that has kept him so much away from it – working in Bosnia in music education, and much else besides – continues.

Medicinal Songs and Dances "contemplates the healing power of music" in a sequence of eight movements lasting half an hour. These accumulate slow ruminations with modal tendencies (several featuring a solo cello), extensive use of quarter-tones, harmonics and other so-called "extended" techniques, fragmentary atonal utterances, and many other elements, to create one of the most moving musical experiences I have had in a long time. Osborne's essential optimism contrasted perfectly with Shostakovich's bleak vision, but made a perfect counterpart to it. The Medicis played throughout with marvellous control, but even more impressive generosity of spirit.

KEITH POTTER

The Angel Series continues on BBC Radio 3 until 12 July