Trivia: "The Three Doctors" was the last appearance of William Hartnell as the First Doctor. The show was written to include all three actors that had played the role as a way of celebrating the show's 10th anniversary. However, by the time the show was made, William Hartnell was in failing health (due to the debilitating ailment, arterial sclerosis). Because Hartnell was so frail, he could only play the part of the Doctor seated in a chair, reading his lines from cue cards. (The plot device of Hartnell being "caught in a time eddy" was written in to explain why Hartnell was only ever seen in the story on TV monitors). Also due to Hartnell's failing health, his contribution to "The Three Doctors" was limited to one day's filming (Monday 6th November 1972) at the BBC's Ealing Studios. "The Three Doctors" was also the last time Hartnell did any acting: he died two-and-a-half years later, on 24th April 1975, aged 68.
Trivia: Some of the 'maggots' used in filming "The Green Death" were in fact inflated Durex condoms.
Trivia: This was the final story to feature Roger Delgado in the role of the Master. He was killed in a car crash in Turkey less than three months after the story's sixth and last episode.
Trivia: For many years, Episode Three of this story only existed in black and white, as the colour master videotape had been wiped by the BBC in 1976. It was eventually restored in colour and released on DVD in 2009.
Answer: TARDISes are generally available for properly authorised use on Gallifrey; they're not usually assigned to a particular Timelord on a long-term basis. The Doctor stole his when he left his homeworld.
Tailkinker ★