The Talons of Weng-Chiang - S14-E6
Trivia: A pile of straw - seen in the road as Weng-Chiang searches for the time cabinet - was placed there to hide a modern (1970s) car which had, despite requests to the contrary, been parked in the road prior to filming, and whose owner refused to move it.
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 ★