|Photo courtesy of RaoulDuke504|
The occasion was 6 November 2015. The event was recorded for us by the excellent video-maker codenamed RaoulDuke504. He told me:
If you would like to experience the atmosphere of the occasion by watching one of the videos (there are several on YouTube), please click here. How often have you heard a five-trombone chorus?! There's one at 5 minutes 26 seconds.