Frazer Hines contracted chickenpox during filming, hence why he loses his face. Hamish Wilson filled in for him.
It was Derrick Sherwin's idea that Lemuel Gulliver should speak only in the words that Jonathan Swift wrote for him.
The horse playing the unicorn had a light brown coat rather than white, and so white blanco from a nearby air force base had to be hastily applied to the animal.
This story is the only time in the series where an actor is replaced and acknowledged as part of the story, being Frazer Hines replaced by Hamish Wilson.
The children who ask The Doctor riddles were inspired by the juvenile heroes of Edith Nesbit's novels, such as 1899's The Story Of The Treasure Seekers.