I was appalled when I read about this. John Taverner was a Protestant who became Orthodox some years ago, and many of his compositions show the influence of Orthodox church music. However, he seems to have left the Orthodox Church and is now a Muslim or possibly Sufi (a Muslim sect that most Muslims consider heretical, but that is very popular among English intellectuals).
It’s disgusting that the Cathedral would let this piece be performed there. I know it’s not a service, but they can’t possibly innocently proclaim that just because it’s a concert, it “doesn’t count.” Would they let neo-Nazis rent the Cathedral to do German Nazi music, and still assert that it didn’t count?
I’ve sung the piece the elegy piece by him that I believe was sung at the Diana funeral. It’s called Song for Athene, and it’s absolutely gorgeous. “May flights of angels lead the to thy rest, Alleluia.” One of the priests of the church I was attending saw us in front of the church with music that had the name of a greek god on it and started to have a problem with it until we assured him it was scriptural.