In the original script, it was the First Doctor, along with Ian, Barbara and Susan, who visited Karfel. Some vestige of this remains in the final version, as Tekker inquires about the Doctor having only one companion with him.
Eric Saward ensured that only one android would ever be present in a given scene, so that only one actor would have to be hired for the role.
Despite its bad reputation, Doctor Who (2005) writer Mark Gatiss has alleged in interviews that his friend Reece Shearsmith is a fan of this story. He said: "For some extraordinary reason he knows the Colin Baker story Timelash backwards. He and his old flatmate used to watch it about five times a week."
Pennant Roberts was concerned about the antagonist nature of the Doctor and Peri's relationship, and the generally mean-spirited attitude of the Doctor. Eric Saward softened much of their dialogue as a result.