100,000 BC - S1-E1
Continuity mistake: When Ian and Barbara enter the TARDIS for the first time, Susan operates the door switch. Later on, when the Doctor electrocutes Ian, he uses the exact same switch.
Who Killed His Royal Highness? - S1-E21
Continuity mistake: When Archie tries to kill Burke with the fireplace poker, Burke knocks him out with a punch that sends him flying over the back of the couch. The stunt man lands on his side, facing the couch. But when Burke looks over at the unconscious Archie, he's lying face up and several feet farther to the left than the stunt man was in the previous shot. (00:48:20)