The Wheel in Space episode 6 exists?
for more information). By the time the Doctor Who episodes were telerecorded, the process had been almost perfected – it involved sophisticated purpose-built devices containing a high-resolution flat-screen monitor which was fed with the pictures from the videotape of the episode in question. Built in to the device was also a high-speed film transport unit (not just a film camera pointing at a TV screen) which pointed at the screen and could therefore make a film recording of the programme. The devices were extremely sophisticated with many pieces of circuitry to control the process and keep the film transport synchronised to the video signal being fed to the monitor.