Continuity mistake: At many points in this story there are problems with the costume that Zoe is wearing...the zip is often jammed part or all the way open. Not only does this leave most of her back exposed, but the position of the zip tends to change position during scenes, as while off camera Zoe tries to pull the zip back up, only for it to open up again minutes later. (It is a little unkind to say it, but possibly the costume was a little bit too tight for Zoe, causing it 'self unzip'?).
Continuity mistake: Patrick Troughton's sideburns keep appearing and disappearing, depending on whether what is being shown is location filming or studio.
Continuity mistake: This story starts off where the previous story ('The Dominators') finished, but Jamie says something completely different to alert the Doctor to the approaching lava flow.
Continuity mistake: The end of episode 7 does not match the reprise of the story at the start of episode 8. The Doctor, Security Chief and guards file into the SIDRAT in a different order.
Continuity mistake: Near the end of episode three, Jamie starts to read the printout. At first, he is reading the printout the right way round. But when we next see him, he seems to be reading it upside down. Then the third time we see him, he is back to reading it correctly (right way up).
Continuity mistake: When the TARDIS breaks apart and the console sent spinning off into space, Zoe is lying on it. In close-ups she lying on her left side facing towards Jamie (who is opposite), but in the distance shots done with small models, she is lying on her right side facing away from Jamie.
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 ★