- Inspiration for the Work: Barbara Clegg's extended family spanned several social strata, and she noted with interest the way that her wealthier relations interacted with their poorer kin. Clegg was reminded of gods toying with lesser mortals, and this led to her creation of the Eternals. She also sought inspiration in The Bible, deriving the prize of Enlightenment from the Tree of Knowledge in the Book Of Genesis. Finally, Clegg seized upon the image of solar winds — actually streams of charged particles ejected from the Sun — to develop the premise of the Eternals racing through the solar system.
- The Other Marty:
- Peter Sallis was booked to play Captain Striker. Sallis did attend one day of rehearsal before a strike started and production dates were charged. Sallis was signed up to a Last of the Summer Wine special and so could not make the dates. So, Keith Barron was cast instead.
- David Rhule was originally cast as Mansell, but he also had to drop out, so singer Leee John replaced him at short notice, despite having no previous acting experience.
- Recycled Script: The plot is similar to that of "The War Games": both involve aliens abducting humans from various points in Earth history and using them for their own ends.
- So My Kids Can Watch: Barbara Clegg wanted to write for the series to please her children.
- What Could Have Been: Amongst those considered for Jackson were Richard Griffiths and Nigel Hawthorne.
- Working Title: The Enlighteners.
- Write Who You Know: Barbara Clegg based the Eternals on some wealthy relatives of hers
- You Look Familiar: Tony Caunter (Jackson) had previously played Thatcher and Morgan.
- You Sound Familiar: Lynda Baron had previously sung "The Ballad of the Last Chance Saloon".
Trivia / Doctor Who S20 E5 "Enlightenment"