The role of Hans Richter is credited to someone called Stephen Oliver, and the entry for this actor also has him appearing in three UK sitcoms in 1985.
However, there was an English composer called Stephen Oliver, perhaps now best known for doing the music for the BBC radio adaptation of The Lord of the Rings (and being the uncle of comedian John Oliver). His wikipedia entry says it is him playing Richter and judging by the photos of him I've found online, it looks like him, but difficult to tell with that big beard he wore for the film. Whether he also acted in the sitcoms, or that was another Stephen Oliver I don't know.
There is a precedence here. The fifties film Magic Fire, also a biopic of Wagner, had composer Erich Korngold as Richter. I wonder whether Oliver was cast because of the links between Wagner's Ring cycle and The Lord of the Rings.