The Sixteen, St John's Smith Square, London <!-- none onestar twostar threestar fourstar -->

Maybe it was the cold, maybe it was the fact that fog had brought the outside world to a standstill, but no one in St John's Smith Square seemed content to just sit and listen. So when Harry Christophers turned his back on his singers before they'd sung a note, and invited the audience to intone "O come, O come, Emmanuel", everybody did, fortissimo. Then it was "Good King Wenceslas", with the gents booming out "Yonder peasant, who is he?" to be answered by the ladies' dainty: "Sire, he lives a good league hence." And what a nice, old-fashioned feeling it was, to sing without fear of being critically listened to.

But Christophers and The Sixteen - on this occasion 18 singers, plus four very versatile instrumentalists - had a serious agenda behind the fun. "Make We Joy" was the title of their concert, that being the opening phrase to the rarely performed medieval Latin carol that concluded the programme.

But what recherché treasures they had unearthed from the archives. A manuscript of 1420 entitled "Hail, Mary, full of grace" yielded up a carol whose raw and yearning harmonies took us into another world; the rebec with which it was accompanied - a bowed instrument imported in the Middle Ages from Muslim lands - reinforced that sense of exotic dislocation. "Angelus ad virginem", found in a 14th-century manuscript in Dublin, gave a different frisson, delivered as it was by a light, high tenor plus lute and harp. We also got magnificence, in the form of highly sophisticated pieces of counterpoint by the French master Jean Mouton and by our own Thomas Tallis, whose "Puer natus est" took the breath away with its bold harmonic audacity.