To protect the secret of Davros' presence in the story, Terry Molloy was credited in part three under an anagram, "Roy Tromelly". Ian Ogilvy was approached for the role of Gilmore, but did not accept; Neil Stacy was also considered. The role went to Simon Williams, who was known for his role as James Bellamy in "Upstairs, Downstairs". Sophie Aldred and Karen Gledhil, who had watched the programme when they were younger, were awed to work with him. Williams had trouble handling the character's gun and also misunderstood a stage direction in the script describing it, which earned him the nickname of "Chunky". This nickname was carried on into the character, with McCoy adding the line, "...why his men call him 'Chunky' I've no idea."