Invasion of the Dinosaurs - S11-E2
Continuity mistake: In episode 2, when the Doctor and Brig arrive at the scene to stun the dinosaur, they leave the stun gun in the jeep. Mike Yates glances down at it and we can see that the sabotage disk is already attached - although he doesn't actually put it on until later.
Invasion of the Dinosaurs - S11-E2
Continuity mistake: In episode 3, Sarah is hit on the head by debris knocked loose by the escaping dinosaur. It hits her on the back of her head or shoulders - but the later bruises and scratches are on her forehead.
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 ★