Continuity mistake: The TARDIS is missing its light the first time it's seen.
Revenge of the Cybermen - S12-E5
Revealing mistake: At the climax of episode four, the Beacon plunges close to Voga and orbits very fast before the Doctor manages to break free. The planetscape that appears on the screen is quite obviously a revolving drum with bits of clay on it.
Audio problem: In episode 3, when the Doctor is squaring off against the drooling madman, it's clear in most of the shots that the sound of the madman's panting is not reflected in his facial and body movements. (00:10:20)
The Monster of Peladon - S11-E4
Revealing mistake: The mines are fairly obvious set constructions. The floor is flat with some sand thrown on. In addition, gaps can occasionally be seen between the floor and the walls or the floor and boulders.
The Talons of Weng-Chiang - S14-E6
Visible crew/equipment: In episode six, when the Doctor and his friends are hiding behind the table and Mr. Sin is blasting it, look out for the pyrotechnic wire dangling from the underside of the table.
Continuity mistake: During Kroll's attack on the refinery, several pieces of the refinery get broken off and then reappear in subsequent shots.
Deliberate mistake: In episode 3 of 'The Web Planet' (titled 'Escape To Danger') watch as one of the Zarbi operators, his vision impaired by the costume, runs right into the camera. So far behind schedule was the recording of this episode, however, that this mistake was retained in the finished episode, as there was no time left for a re-take.
Other mistake: Near the end of episode 5, Stevens is reading out previous numbers of slave units and B.O.S.S is telling him the new ones. For New York, the previous figure was 7203 and the new figure 7580. However, for Moscow the previous figure was 10003 (ten thousand and three), and the new figure is 110098 (one hundred and ten thousand and ninety-eight), which is a big difference.
Continuity mistake: In episode 2, when the Russian soldier is enticed into the water by the now-Haemovores Jean and Phyllis, watch his helmet, which he drops into the water as he moves towards them. When the camera angle changes to a shot of him from the front, we see his helmet slowly drift from directly behind him out to the right of screen. Then we cut to a shot of Jean and Phyllis, then back to the soldier - whereupon his helmet again drifts from directly behind him off to the right. Finally, when the other Haemovores drag him down into the water, look behind him and you'll see the helmet, sitting on the beach well above the waterline...
Earthshock - S19-E6
Revealing mistake: Just before the Cyberman fires on the console, you can see Adric trying to keep as far away from it as possible before it explodes. (01:35:05)
Revealing mistake: How did Rubeish's glasses manage to improve his chronic shortsightedness when they are obviously plain lenses?
The Monster of Peladon - S11-E4
Revealing mistake: In the climactic fight at the end of episode four, the face of the Doctor's stunt double can be seen.
Continuity mistake: When Toos is being hunted by a robot, she shuts the door on its hand. When you see this scene from the inside of the room, the robot's hand is trapped at a different place to the next shot, which is from outside the room.
Deliberate mistake: The character of "Chicki" is played by a completely different actress in episode 4 to the one who played her in episode 1.
Underworld - S15-E5
Continuity mistake: When the Doctor races out of the R1C with the fission bombs in episode four, Leela follows, carrying a shield gun. She steps into the cave and is only holding her knife. Later, she has her shield gun back.
Genesis of the Daleks - S12-E4
Visible crew/equipment: Just after The Daleks move past the Doctor and the female Thal soldier in the corridor, a piece of lighting equipment is reflected on the wall behind her. (00:08:00)
The Monster of Peladon - S11-E4
Continuity mistake: In episode six, the same extra is killed by both Azaxyr in the ambush and by Eckersley later on.
The Monster of Peladon - S11-E4
Revealing mistake: Near the end of episode six, when Aggedor is falling dead to the ground, the clothes of the man inside the costume can be briefly seen in a gap between Aggedor's leg and foot.
Revealing mistake: The footage of Kroll eating Harg is obviously reversed, as evidenced by the fact that the smoke from the pipe is heading into it, whereas in every other shot it's flowing out of it. (00:23:00)
The Armageddon Factor - S16-E6
Continuity mistake: In episode 2, just after K-9 begins blasting the door, look behind Romana and notice that you can see the TARDIS - which supposedly left in the previous scene.
Answer: It was never destroyed on-screen; it was intact at the end of the TV movie, and destroyed by the start of the 2005 series. It was destroyed in the novel "The Ancestor Cell," but in a completely different manner to what happened in the series.
DaveJB