My Doctor Who rewatch has brought me to The Leisure Hive (which is better than I remembered) and Meglos (which isn't), both of which feature incidental music of way above average quality by Peter Howell. A bit of googling reminded me that he was the author of the amazing Greenwich Chorus, of which there doesn't seem to be a decent online version. There is, at least, this audience footage of a live performance of the piece by Howell:
Click to view
Fantastic.