I think I mentioned this before, I was in London last year in December and I like to just pop into any interesting looking churches I see when I travel, to look around and light a candle when possible.
On two occasions the churches I visited were having rehearsals of their holiday shows. So by quietly entering and sitting I could hear some lovely music in a lovely setting. Yet another reason to check out that church you are walking past. You should also look for brochures in the lobby about upcoming performances.