For the climax of the tale, the location of TCC Condensers in North Acton was selected as the Ryden Plastics factory. The Doctor Who (1963) team had used this in 1968 to represent the Cybermen-invaded International Electromatics premises (in a story scripted by Derrick Sherwin), and the following year it featured as Auto Plastics in "Spearhead from Space" where UNIT battled the Autons (the series by then produced by Sherwin). Sherwin also produced this episode, in 1971.