- Actor Existence Failure: Geoff Noble's actor, Howard Attfield, died after he was set to return in series 4. Therefore, Bernard Cribbins' character Wilfred Mott, introduced in "Voyage of the Damned", was used instead, and filled the role he was supposed to undertake and quietly re-written as Donna's widowed granddad. The scenes with Geoff were shot and completed, but re-shot with Wilf when Attfield passed away, and Donna's father was mentioned to have died at some point after the events of the wedding. Howard Attfield's scenes as Geoff Noble are included as an extra on the DVD set with a nice intro from RTD.
- Blooper: This episode has one of the most noticeable continuity errors in new series history: during the scene with the Doctor and Donna in the window-washing cart, the cable cut by Miss Foster switches sides between the shots of her on the roof and the shots of the Doctor and Donna below.
- Development Gag: There is a journalist called Penny Carter, which was the name of the intended new companion for Series 4 until it turned out that Catherine Tate wanted to return to Who.
- Harpo Does Something Funny: For the scene where the Doctor and Donna are reunited on either side of soundproof glass and thus have to mime their conversation, the script gave the lines they wanted Donna to mime and then the director let Catherine Tate and David Tennant go to town. The result is one of the most gut-bustingly funny scenes ever to hit television.
- Not Screened for Critics: Donna's conversation with Rose Tyler was removed from the preview copy of the episode to hide her return.
- What Could Have Been:
- In the first draft, the initial confrontation between the Doctor, Donna and Miss Foster was to have happened in the cradle, but budgetary and logistics problems meant the scene was moved to the sales cubicles area (and the Doctor's "sonic screwdriver plus sonic pen equals massive sonic feedback" diversion added).
- Russell T. Davies considered setting the story in suburban London, with a spaceship sealing off a section of the city under an enormous dome while an alien was hunted through the streets. The dome aspect was dropped because it was used in The Simpsons Movie.
- Miss Foster was originally called Miss Rattigan. It was changed because Davies felt that it better encapsulated her motherly role, and the Rattigan name would instead go to Luke Rattigan in "The Sontaran Stratagem".
- When it was clear that Howard Attfield would be unable to be in the episode, Davies considered writing his character's death into the story arc, with Donna becoming a stronger person after dealing with the loss of her father.
- At one point, the story was set in a dilapidated old house which would hide a portal to another planet which had been overrun with vicious, dog-like Vorlax. The last survivors of this world had opened the portal to Earth in order to rid their world of the invaders.
Trivia / Doctor Who S30 E1 "Partners in Crime"