Miss Hawthorne correctly states that the Witchcraft Act of 1735 was only repealed in England in 1951 with the enactment of the Fraudulent Mediums Act. The last successful prosecution had been in 1944.
This episode was watched by 8 million viewers on its original transmission.
The colour master videotape of this episode was wiped by the BBC in the 1970s and the BBC only held a 16mm black and white telerecording. A poor quality colour NTSC version taped on a home recorder also existed. The episode remained only in black in white until the 1990s, when the colour signal from the NTSC version and the black and white telerecording were used to create a new colour master on D3 digital tape.
First of Two Pertwee serials that Christopher Wray has minor roles in.
The Doctor asks Jo if she failed Latin as well as Science. However, at their first meeting Jo shared that she is as a fully qualified agent, and that she took General Science at A level. Later in that episode, The Doctor mentioned that he thought she took an A level in science. Jo confesses that she didn't say she passed.