Revealing mistake: In episode 6, during the generally poor fight sequence between the Brigade Leader and Greg Sutton, Greg's first punch to the face misses the Brigade Leader by miles. (00:19:10)
Revealing mistake: In episode one, a wall wobbles as Benton hammers a nail into it.
Revealing mistake: In episode 6, when the Brigade Leader shoots the Primord Stahlmann, he falls down but no bullet holes are made in his costume. Thanks to Producer Barry Letts for spotting this one on the DVD commentary. (00:17:00)
Revealing mistake: In episode 5, when the Doctor kills the Primord with the fire extinguisher, he says 'he's dead this time' but the Primord is breathing. (00:07:10)
Revealing mistake: In episode 3, when the Doctor is squaring off against the drooling madman, the madman is inside the perimeter railings. When the soldiers shoot him and he 'falls', however, he has moved outside the railings, enabling the stuntman to jump safely. (00:10:40)
Revealing mistake: When the Doctor falls out of the TARDIS, near the beginning, he nearly manages to pull off the entire TARDIS door.
Revealing mistake: When Stahlman is killed - the second time - the shot of his green primord face reveals the actor's unpainted neck under his beard.
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 ★