Revealing mistake: When Pralix lifts the spanner in the composite shot, bits of debris lift up with the spanner.
Revealing mistake: K-9 has a bit of difficulty in the mansion in episode two. The thread pulling him is visible and Baker has to help him over a flagstone.
Revealing mistake: Zadek claims the water door into Castle Gracht is a foot thick. But it is obvious when the Doctor crawls through that it is paper thin.
Revealing mistake: When K-9 is cutting through the wall of the hut, the cut overtakes his laser at one point.
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)
Revealing mistake: One of the stones wobbles when a crow lands on it in episode one.
Destiny of the Daleks - S17-E1
Revealing mistake: In episode one, when the Doctor and his companion hear rumbling and the ground moves beneath their feet, when they step away you can see that they are standing on different ground than before, and it's not shaking. (00:08:00)
Destiny of the Daleks - S17-E1
Revealing mistake: When the Doctor and his companion are running past explosions in the sand, you can see the scrape marks from where the effects team covered up the holes containing the charges. (00:13:00)
Destiny of the Daleks - S17-E1
Revealing mistake: Right after Davros yells "The Daleks will rule the universe," in Episode 3, one of the Dalek operators accidentally starts to lift the top off his Dalek before the scene ends. (00:17:35)
Revealing mistake: In episode 2, when Scaroth locks the Doctor, Romana and Duggan in the basement dungeon, and Duggan lights the lamp, notice that Tom Baker is standing between that lamp and the actual stage light used to brighten the scene. So, as the lamp is lit in front of him, Tom Baker's BACK (and not his front) glows bright under the increased illumination.
Revealing mistake: In episode one, Scaroth's 'Jagaroth skin' on his wrist flaps about. Either that's a badly fitting piece of costume...or he's suffering from severely peeling skin.
The Creature from the Pit - S17-E3
Revealing mistake: Torvin, stunned by K9, turns before falling, as if looking for somewhere comfortable to land; and the guard who goes to attack K9 and Romana acts very strangely: he stops and curls up before K9's blast hits him, almost as if he knows what is going to happen next.
The Creature from the Pit - S17-E3
Revealing mistake: Before the TARDIS console explodes (as Erato is weaving his shell around the neutron star), Tom Baker casts a sharp look over his right shoulder...no doubt looking to see if the ground was clear where he was due to fall.
The Creature from the Pit - S17-E3
Revealing mistake: Just as the Doctor asks where the TARDIS has materialised, watch the control console wobble. However, isn't it strange that the hat-stand in the TARDIS console room remains upright thoughout...so why does the console wobble, and the hat stand not move in the slightest?
Revealing mistake: Watch the Mandrells closely, especially in the later parts of the story: one of them seems, at one point, to have forgotten to zip up the back of his costume.
Revealing mistake: In the very first shots of this Doctor Who story, it is obvious that the "Empress" Spaceliner is a model - you can even see the stick that holds the model in place.
Revealing mistake: Geoffrey Hinsliff (playing Fisk) accidentally refers to Tryst as "Fisk" at one point.
Revealing mistake: In episode 1, watch out for the wires pulling K-9 along the beach. (Unlike a real dog, K-9 didn't take well to the soft sandy surface and sank into the sand. Pulling K-9 along on wires provided an illusion of movement when the motor inside wasn't up to the job).
Revealing mistake: The Grove is one of the most obvious indoor sets masquerading as a lush outdoor environment. The sound the actors' feet make on the floor is especially unforgivable.
Revealing mistake: When the Keeper is on the TARDIS, he asks to borrow the screen. But on the upper left corner, you can see it over where it's meant to be.
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