This was an event so surreal you could believe Magritte had a hand in its design. To launch the Southbank Centre's Nono festival, we heard not a note by the Italian modernist but instead a Renaissance choral masterpiece, performed in Westminster Cathedral.

Of course there's an explanation, of sorts. Nono was Venetian. Monteverdi wasn't, but he spent his best years in that city, in charge of music at San Marco where his 1610 Vespers may or may not have been performed. Nono's vast Prometeo, coming to the UK soon, was influenced by Monteverdi's spatial inventions.

So far, so woolly. This wouldn't matter had the performance, by Westminster Cathedral Choir and the New London Consort conducted by Martin Baker, been good. Yet it's hard to imagine a more ill-judged or slipshod account, which also failed to grasp the acoustic challenges of the reverberant 1903 building.

To suggest, as the programme note did, that St Mark's and Westminster are similar because they're cavernous and have mosaics is lazy and inaccurate. Architecturally they're virtual opposites. St Mark's is compact, with all the action concentrated at the centre. Westminster is open, with a long, wide nave and the focus at the east end. The impact on musical performance is crucial.

Elgar or Rachmaninov work well. But Monteverdi's delicate rhapsodies and antiphons are lost to the heavens unless you strengthen musical forces, as John Eliot Gardiner has done here in the past.

>One solution might be to perform mid-nave, so everyone could hear. Last night the sounds shuffled through this great building like a Mexican wave, arriving wan and etiolated instead of muscular, buoyant and joyful.