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).
The Romans - S2-E4
Factual error: The geographical references in this story are somewhat suspect. Assissium is the modern town of Assissi, some 70 miles north of Rome and the same distance east from the sea. The Great Fire of Rome took place in July 64AD.
Plot hole: Leela's decision to stay with Andred is very sudden. They barely speak during the serial.
Revealing mistake: When Stahlman is killed - the second time - the shot of his green primord face reveals the actor's unpainted neck under his beard.
Planet of the Spiders - S11-E5
Continuity mistake: In episode two, Lupton steals a boat, throwing the pilot into the water. Moments later, we see him struggling with the pilot again - who is perfectly dry.
The Monster of Peladon - S11-E4
Continuity mistake: In episode six, the Doctor is using the Aggedor statue to fight The Ice Warriors. The door to the refinery was partially destroyed by The Ice Warriors earlier. But in every shot of Aggedor appearing or re-appearing, the door can be seen intact at the edge of the shot.
Genesis of the Daleks - S12-E4
Revealing mistake: When Ronson is killed by The Daleks, you can see Ronson reacting a little too soon to the Dalek laser. (00:14:40)
The Talons of Weng-Chiang - S14-E6
Audio problem: In episode five, when the Doctor and Leela are in the opium den, the Doctor's lips do not match his spoken dialogue.
Factual error: In episode one, Abraham Lincoln seems to have affected a southern accent and put on some weight.
Time-Flight - S19-E7
Factual error: The Pleistocene Period began around 1.8 million years ago, not 140 million years ago as stated.
Genesis of the Daleks - S12-E4
Revealing mistake: In episode 6, when the Thals detonate the charges, smoke is seen coming through the door before the detonator is pressed down. (00:19:40)
The Caves of Androzani - S21-E6
Continuity mistake: When the Doctor is climbing through the tunnel to the Queen bat, note the question mark on his lapel: the image is reversed.
Earthshock - S19-E6
Revealing mistake: When Lieutenant Scott kills the second Cyberman on the bridge, he starts falling down way too early.
Invasion of the Dinosaurs - S11-E2
Revealing mistake: When Grover and Whitaker struggle over the time machine at the very end of episode six, the console wobbles and jerks as though it were very lightweight.
Audio problem: About 10 minutes into episode 1, the sound of a pencil being dropped and rolling across the studio floor can be heard. (00:10:00 - 00:11:00)
The Sea Devils: Episode Four - S9-E12
Plot hole: The Doctor and the Master both surface in bright orange diving suits and are the only two wearing them. But when the supposed body of the Master is dragged out it is also wearing an orange diving suit, and the Doctor and Master are still wearing theirs, so a third suit appeared from nowhere.
Battlefield - S26-E1
Continuity mistake: When the roof falls on Ace and Shou Yuing, Ace's face gets covered in dark streaks, which mysteriously disappear soon afterwards.
Earthshock - S19-E6
Revealing mistake: The "dead" crewmembers at the end of episode two can be seen breathing.
Revealing mistake: In Episode 3, when Dask is cutting the wires, the second explosion happens too early.
The Caves of Androzani - S21-E6
Revealing mistake: When Peri falls into the spectrox nest, watch for her to reappear as she bounces off a mattress.
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