Well, he wasn't an actor. Dr Magnus Pyke was a real scientist who happened to be great on TV, and that made him a familiar face on British information programs. Americans probably know him (and probably not by name) only because of Thomas Dolby, but he was easily better known to Brits than Dolby at the time, and his lengthy 1992 obituary in the British Newspaper, the Independent, doesn't mention Thomas Dolby or his song at all, not that surprising, because the song was not a hit in Britain.
Magnus Alfred Pyke, food scientist and broadcaster, born London 29 December 1908, OBE 1978, Principal Scientific Officer (Nutrition) Ministry of Food 1946-48, Deputy Manager Distillers Co Yeast Research Outstation 1949-55, Manager Glenochil Research Station 1955-73, Secretary and Chairman of Council British Association for the Advancement of Science 1973- 77, books include Manual of Nutrition 1945, Six Lives of Pyke 1981, married 1937 Dorothea Vaughan (died 1986; one son, one daughter), died London 19 October 1992.
Here's Thomas Dolby telling funny stories about Dr. Pike at a 2011 concert