Revealing mistake: When Ace and Susan are sitting underneath the huge pipe about to be executed by the Fondant surprise, it's obvious that the actresses aren't sitting directly underneath the pipe, but slightly behind it.
Revealing mistake: In episode one, as the Doctor is repairing the buggy, one of the patrol runs on too soon, realises that he's come in ahead of his 'cue', and runs back.
Revealing mistake: When the Doctor taps the ice crystals, they wobble instead of breaking.
Remembrance of the Daleks - S25-E1
Revealing mistake: When the Doctor slides with his umbrella from Coal Hill School to the Dalek spaceship, he is obviously not played by Sylvester McCoy. He is much too tall.
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 ★