At Doctor Who fan events, Nicholas Courtney frequently recounted an incident which occurred during shooting of the scene with the revelation of the Brigade Leader and his eyepatch. The scene begins with Courtney's back to the camera (and to all the other actors), and then he spins around in his swivel chair to reveal the Brigade Leader's visage and eyepatch. When the scene was shot, Courtney spun around to discover that all the other actors and crew members were also wearing eyepatches.
While filming the chase scene in the parallel universe, Jon Pertwee accidentally ran over stuntman Alan Chuntz. He gashed his leg, requiring eighteen stitches. When Pertwee saw the wound and learned he caused it, he became sick and almost couldn't carry on filming until a few hours later. He even went as far as buying Chuntz's wife a gift to apologise for the accident.
Caroline John enjoyed her role as Section Leader Elizabeth Shaw and said that it was fun playing "baddie" Liz. She also says she hated doing the scenes when she was playing the normal version because it was boring compared to being the parallel character.
The RSF ranks of Brigade Leader and Section Leader (the ranks held by Lethbridge-Stewart and Liz Shaw in the fascist society on the parallel Earth) are actually English translations of Brigadeführer and Scharführer in Nazi Germany's SS. Benton's rank, "Platoon Under Leader", is similar to Unterscharführer which was the SS equivalent of Sergeant, which is Benton's rank in UNIT. The Brigade Leader's shoulder rank tabs feature leafs rather like those in SS senior rank insignia (but arranged differently)
Originally, it was Section Leader Shaw who interrogated The Doctor. To Caroline John's displeasure, Nicholas Courtney convinced Douglas Camfield and Barry Letts that The Brigade Leader should do it.