This marks Tim Pigott-Smith's television debut. He was reportedly paid £60 a week for his role as Captain Harker here and in The Claws of Axos: Episode Three (1971). He would later play Marco in The Masque of Mandragora: Part One (1976).
The color master tape of this episode was wiped by the BBC in the 1970s and the BBC only held a 16mm black and white telerecording. However, in 1979 an NTSC color tape was recovered from Canada and converted back to PAL for British broadcast.
This episode was watched by 8 million viewers on its original transmission.