Inferno (Doctor Who) - Production

Production

Don Houghton came to Terrence Dicks with an idea for the story based on the real life Project Mohole. A smaller budget for the serial drove the idea of a parallel world, where the studio could use the same actors in multiple roles. Despite Douglas Camfield receiving sole credit as director, Episodes 3-7 were directed by producer Barry Letts after Camfield had a minor heart attack on April 27, 1970. Letts later stated that Camfield's preparations were so meticulous, that he just followed the other man's plans anyway. Camfield remained credited as director, as BBC regulations at the time forbade any person from being credited for more than one production role, and they did not want Camfield's illness to become widely known, lest it harm his career.

Derek Ware did not actually perform the scene where the mutated RSF Trooper Wyatt is shot and falls to his death from the top of one of the cooling towers, in case he was injured, as he was also needed for studio recording. His place was taken by Roy Scammell, who also played the soldier who fires the fatal shot. Ware also stated in an interview that Scammell had already signed the contract to do the fall before Ware had been cast as Wyatt. At the time it was filmed, the fall was the highest fall ever performed by a British stuntman. John Levene's portrayal of Benton as a Primord was inspired by Richard III (so nicknamed because of the Primord creature's hump).

Caroline John enjoyed her role as Section Leader Elizabeth Shaw and says that it was fun playing "fascist" Liz. She also says she hated doing the scenes when she was playing the normal version because it was boring compared to being an evil character. She was particularly upset though about the scene in which Shaw shoots Brigade Leader Lethbridge-Stewart, as she was pregnant at the time. As a result, the scene was recorded with the weapon fired from out-of-shot, after which Shaw was shown returning the gun to her holster.

During the scenes set on the parallel Earth, images (supposedly) of the British Republic's dictatorial leader are seen on posters. The image used is that of Visual Effects Designer Jack Kine, in homage to the 1954 BBC adaptation of Nineteen Eighty-Four where the face of Big Brother was Head of Television Design Roy Oxley (Kine had worked on the visual effects for that production).

Episode 6 has a small damaged section on the domestically recorded videotape, which the Doctor Who Restoration Team replaced by painstakingly recolouring the appropriate section of the existing b/w film recording.