- Acting for Two: Bernard Holley (Axon Man) also provided the Voice of Axos, but was uncredited on-screen.
- Creator Backlash: Bob Baker was unhappy at the inclusion of the Master, as he felt that he didn't fit well in the established plot.
- Fake American: Welsh Paul Grist as American Bill Filer.
- Serendipity Writes the Plot: During location filming, the weather proved highly variable, ranging from snow at the start of the week, through fog and finally to sunshine on the final day. To explain the inconsistency, Terrance Dicks assigned a new line of dialogue to Corporal Bell which noted that Axos' arrival had prompted freak weather conditions.
- What Could Have Been:
- Bob Baker and Dave Martin originally pitched this as a seven-part story featuring the Second Doctor. It involved evil aliens who land in Hyde Park in a skull-shaped spacecraft, and featured spaceship battles and even a giant carrot crashing into the park. The production team loved the story, but had it scaled down on account of impracticality and budget.
- The use of Axonite was to have been demonstrated using a rat instead of a toad.
- Scenes cut from the script include a Meet Cute between Jo and Bill and the Brigadier daydreaming of having Chinn taken out the back and shot through the head.
- Working Title: The Gift, The Friendly Invasion, The Axons and The Vampire From Space.
- You Look Familiar:
Trivia / Doctor Who S8 E3 "The Claws of Axos"