- Cast the Expert: Amongst the members of Wholeweal, Jessie was played by a real flautist named Jessica Stanley Clarke. She was also a member of the prog-rock band Marsupilami, who had once toured with Deep Purple; later known as Jekka McVicar, she became a well-known expert on organic gardening.
- The Danza: Mostyn Evans as Dai Evans.
- Romance on the Set: Stewart Bevan (Cliff Jones) was Katy Manning's real-life boyfriend at the time of shooting. Michael E. Briant was reluctant to invite Bevan to audition, fearing the on-set ramifications — especially considering how upset Jon Pertwee had become when he learned that Manning was leaving. However, Bevan ultimately proved to be the only suitable choice for the role.
- Throw It In!: John Levene ad-libbed Benton's reference to two UNIT soldiers as "Dicks" and "Betts" in honour of the production team.
- What Could Have Been:
- Global Chemicals was originally named Universal Chemicals. It was then United Chemicals, until it was discovered that a real company with that name existed.
- Ralph Fell was originally named Charles. This was changed to avoid confusion with a real-life petroleum company executive.
- It was briefly thought that Yates' role in the latter stages of the serial might be given to Benton instead, but this idea was not pursued.
- A Wholeweal member nicknamed "Face" was excised from the script and the relevant dialogue instead allocated to Nancy.
Trivia / Doctor Who S10 E5 "The Green Death"