Continuity mistake: After shooting the two guards near the beginning of episode three, K-9's nose blaster retracts twice - one in close-up, once in medium shot.
Continuity mistake: The Gatherer gleefully states that being on the roof is a fine of 500 talmars. Later, Cordo says it is 5 talmars.
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 ★