Revealing mistake: In episode two, when Leela and Mandrell are arguing about raiding the Correction Center, the camera bumps against something.
Underworld - S15-E5
Revealing mistake: The CSO caves are awful throughout, but one of the worst incidents is in episode three when Leela talks to Idas about a revolution and they both run right through a rock.
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.
Underworld - S15-E5
Factual error: While it's true the centre of a planet would have no net gravity, the weightless condition would be everywhere, not concentrated in a convenient shaft.
Underworld - S15-E5
Revealing mistake: The pacifier devise is obviously a stage lamp.
Plot hole: In the middle of chasing the Doctor, Stor abandons the idea of controlling Gallifrey in favour of destroying it for no readily apparent reason.
Continuity mistake: When the Doctor shoots Stor with the De-Mat Gun, the flash starts on Stor's left-hand side, engulfs him, then jumps substantially to the right before whiting out the frame.
Plot hole: Leela's decision to stay with Andred is very sudden. They barely speak during the serial.
Continuity mistake: The Doctor has his scarf when he first meets with the Vardans. When he returns to the TARDIS, it is on the coat rack.
Visible crew/equipment: When Romana brings the Tracer near the jewel cabinet in episode one, the wire powering the prop can be seen at the bottom of her hand.
Deliberate mistake: Tom Baker has some wounds on his lip (caused by actor Paul Seed's dog) which appear in episode one and four in the TARDIS scenes and disappear for the rest of the episode.
Plot hole: After Romana and the Doctor hide in the relic room, the Captain enters, then bends down to inspect the door that conceals the Shrivenzale. Unfortunately, the actor turns to his right when he does so, which make it rather odd that he doesn't see the white-clad Time Lady standing right in front of him.
Deliberate mistake: The shot of rocks falling in episode four is used twice - once when Unstoffe is shot, once after the captain fires the cannon.
Revealing mistake: When the Doctor sabotages the inertia neutralizer, the wall wobbles.
Revealing mistake: The TARDIS manual Romana shows the Doctor quite obviously has a couple of hand-written pages jammed in so that they can be easily ripped out.
Revealing mistake: There are times in this episode where the strings holding up the Captain's trophies are visible. Additionally, the "billions of tons" of planet sways back and forth slightly.
Factual error: While gravitational forces can be "balanced" between planets at very specific points, the notion of balancing them completely to cancel each other out everywhere, as depicted in the Captain's trophy room, is nonsense.
Revealing mistake: The queen, suspended in the last few moments of life, can be seen to breathe rapidly and blink.
Plot hole: Mr. Fibuli reports that the aircar the Doctor tried to steal is immobilized. Yet somehow, K-9 is able to activate it.
Continuity mistake: K-9 looks slightly different in the scene in which he's spinning inside the TARDIS: notice the pattern on his collar.
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