CANTANDUM is a Westminster-based chamber choir with numerous things in its favour, not least spirit of attack, excitingly good enunciation, and subtle dynamic grading.

But what one admires, above all, is the flair that its founder and conductor, Gilly French, brings to the choir's programming. How many such ensembles, I wonder, would include in their repertoire d'Astorga, Caldara, Biber, Legrenzi, Bononcini, Carissimi, Charpentier, Guerrero, Michael Haydn, Jakob Handl (as well as G. F. Handel), Thomas Linley, Marenzio, Manchicourt, Mundy, de Rore, Scarlatti, Steffani, and Zelenka?

It is the kind of material that one might scour the music cupboards of Westminster Cathedral or, again, the Abbey for. Wherever Cantandum perform - St Mary's, Bampton, in Oxfordshire is a favourite venue - they bring the same verve and musical common sense, founded on competent preparation and a patent musical intelligence in all their performers.

At this intimate concert, tucked into Westminster School's beautifully framed Ashburnham Garden - once the monks' refectory, and a meeting-place of the medieval House of Commons - it was the turn of Fux. Johann Joseph Fux (1660-1741) was a contemporary of Purcell: far longer lived, he was a musical giant, a composer, and a musical theorist of whom scandalously few hear nowadays. One or two recordings - his Missa Corporis Christi (on CPO), his oratorio St John the Baptist (on Thorofon), or his Kaiserrequiem (on Deutsche Harmonia Mundi) - keep his name alive as a composer of vigorous, beautifully turned sacred music; yet they scarcely do justice to Fux's stature as the Viennese court composer and Kapellmeister at the turn of the 18th century.

Nisi Dominus, Fux's setting of Psalm 127, after perhaps a hesitant start, grew magnificently as Gilly French brought punch and teeth to the canonic unfoldings that are a characteristic of Fux's Baroque manner. Increasingly assured and unnervingly beautiful, it was like hearing some wonderful after-echo of Praetorius, whose Christmas music, garishly forward-looking, was gloriously recorded by Westminster Cathedral in David Hill's day.

Cantandum's experience in singing Schütz (his Deutsches Magnificat, notably) shone through here. Individual solos (e.g. an impressive bass; their low voices were strong as a whole) or pairings (two tenors), and one sensational section for single soprano ensured that this neglected Viennese genius got the best possible airing.

In some respects, the concert's second half excelled even this. Haydn, also a legend at St Stephen's Cathedral and the Imperial Court, was born just nine years before Fux died. His Theresienmesse, like the Heiligmesse and Harmoniemesse - all treasures from Haydn's final years - tends to lose out to the popular, thundering war-related masses. But Cantandum, with heads impressively up, watching the conductor, benefited vastly from French's gift for choosing exactly the right pacings, and here, at least, maintaining them to perfection. Her warm beat in the Kyrie set the standard for continuous excellence; and her shelving of the baton for a sensuous "Gratias agimus", and at the Sanctus, produced some of the best results.

Again, one was impressed that so many choir members could perform such appealing, articulate solos. Yet not just the voices: French served up sturdy brass, stylish clarinets, and one wonderful transition for string quartet, plus echoes of Figaro and Don Giovanni. One sensed that Haydn in his crepuscular years learned and borrowed from later Mozart, just as the refinement of French's shaping, often crystalline, brought to mind that harbinger of the classical era Pergolesi.

The small orchestra's leader, John Crawford, with his long bowings, produced some of the richest and most beautiful sounds of the evening. If the Agnus Dei needed to be freed up a little, the final "Dona nobis pacem", gorgeously counterpointed by trumpet, was one of the jewels of a constantly rewarding concert.