John Wiles and Donald Tosh greatly disliked the Doctor Breaking the Fourth Wall to give us a Christmas message and would later claim that this was an unplanned improvisation by William Hartnell, although the fact that the line appears in director Douglas Camfield's camera script proves otherwise. (It was common practice for BBC shows, even dramas, to directly address the audience like this for Christmas episodes.)
Moreover, the two were also annoyed having to finish a project started when Verity Lambert was still on the show, and also trying to work with Terry Nation's underwritten scripts.
Fake American: The second half of Episode 7 ("The Feast Of Steven") takes place on a 1920s Hollywood film set: the American characters are played by British actors: Sheila Dunn as film star Blossom Lefavre, Leonard Grahame as co-star Darcy Tranton, Royston Tickner as director Steinberger P. Green and Mark Ross as fellow director Ingmar Knopf.
Hostility on the Set: This is where William Hartnell and John Wiles’ relationship reached its breaking point. Hartnell’s worsening health and previously-seen stubbornness was so prevalent that it caused Wiles (and Tosh with him) to resign as producer and be replaced with Innes Lloyd.
The BBC currently hold Episodes 2, 5 and 10 in the archive. The other 9 episodes remain missing; Episode 4 may still exist, as it was lost after being loaned to Blue Peter for use in a featurette about the show's tenth anniversary. (The discovery of Episodes 5 & 10 was the most remarkable recovery of any missing episode, as the film cans were found in the basement of a church in London. Precisely what they were doing there has never been ascertained, but apparently the basement was often hired for storage space.) The audio for all 12 episodes exists thanks to fan recordings, and a few on-set and publicity photos of the story also exist as well as some off-air photos of Episode 7, but no telesnaps as producer John Wiles did not use John Cura's telesnaps service.
Episode 7 "The Feast of Steven" is the only Doctor Who episode generally believed to be irretrievably lost— the BBC wiped the master tape soon after broadcast, and it wasn't offered for sale to overseas broadcasters as it was a Christmas episode intentionally written to be inconsiquential to the main plot. However, according to Restoration Team member Paul Vanezis, it's possible that a telerecording was made of this episode in the absence of instructions not to make one, simply as a matter of course, which is how the unaired "pilot" version of "An Unearthly Child" survived. Therefore, there is a remote possibility that the episode could exist.
Funnily enough, "The Feast of Steven" is the missing episode for which we have the most extensive visual record; no telesnaps exist for any of the episodes, but Robert Jewell, who usually worked as a Dalek operator, was cast in that episode as Bing Crosby the clown. For this reason, he took his own off-air photographs, which are the only surviving visual record.
No Export for You: "The Feast of Steven" was never broadcast anywhere or at any time except in Britain on Christmas Day. When the serial was sold overseas it was as an 11-episode story, with "Feast" omitted. It would not have made sense to air except in the context of Christmas, and was written to deliberately be totally inconsequential to the overall story. The only reason it was even produced was because Christmas happened to fall on a Saturday that year and the production team decided to put out an episode as per usual, but it was believed nobody would be watching.
Reality Subtext: The Doctor's line "It's a madhouse - it's full of Arabs" feels like William Hartnell's alleged bigotry bleeding into the script.
Contrary to what is sometimes claimed, the Doctor's Breaking the Fourth Wall at the end of "The Feast of Steven" was not improvised. It was common practice for festive programmes, even dramas, to have someone wish the viewers a happy Christmas at the time. However, the claim that it was ad-libbed probably came about because in Donald Tosh's finished script, the Doctor doesn't explicitly acknowledge the audience. The line was changed in-studio by director Douglas Camfield (according to him, at Hartnell's request) and appears in Camfield's camera script. (Though still not quite as delivered - Camfield's script says "Incidentally, a happy Christmas to all of you, too", rather to "to all of you at home.")
Played completely straight however by Mavic Chen troubleshooting his loudspeaker, which was done by Kevin Stoney.
The original intention was that the police station scenes of "The Feast of Steven" would make fun of Z Cars, a popular crime drama at the time. However, the production team of that show vetoed the idea, and producer David Rose denied it on the grounds of how out-of-place the parody would be in a drama series.
A Spin-Off series featuring Space Security vs the Daleks was contemplated by Terry Nation, although the BBC were less keen. Sara Kingdom was intended to be in it.
Originally Vicki was supposed to be the one killed off in "The Traitors" instead of Katarina. Katarina got the axe because writers found her character too limited and difficult to develop.
Taranium was originally named Vitaranium, but was renamed because Hartnell had trouble pronouncing it.
Working Title: The Daleks (Part IV) and Battle of Wits.
Jean Marsh had previously played Princess Joanna in the same story.
Miscellaneous Trivia:
An interesting loose end regarding "The Feast of Steven" is "Albert Barrington", who played the real Professor Webster whom the Doctor had been mistaken for earlier. There's absolutely no other documentation of this actor, and nobody seems to remember what they shot and no photos of the scene exist. Loose Cannon, for their reconstruction, used images of William Hartnell, based on the theory that it may have been a cover name for Hartnell playing a double role. An "Albert Barrington" also played a small role in an episode of Z Cars in early 1967; that episode was also directed by Douglas Camfield and is also missing, but raises the possibility it was a Creator Cameo by Camfield himself (though it doesn't address how the Doctor could be mistaken for a man played by Camfield, who was in his mid-thirties).
Episode 5, "Counter Plot", caught the attention of none other than Stanley Kubrick, who was so impressed by some of the effects that his production office contacted director Douglas Camfield asking how they were pulled off, hoping to replicate them for 2001: A Space Odyssey.
