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.
Revealing mistake: The Filer vs. Filer fight in the lab is very amusing, not only because of the several glimpses of the stuntman doubling for Filer, but also because of the way the "metal" railings around the set wobble as they slam into them.
Revealing mistake: In the UNIT tracking room, there is a flimsy railing behind the radar operators that Chinn knocks as Yates leads him off to the "direct" phone line, causing it to wobble badly. The Doctor then deals the railing another blow as he comes up to look at the console.
The Daemons - S8-E5
Revealing mistake: When the Brigadier crosses over to the RAF and the plane, you can see the plane is a model with a stick to control it just under the nose.
Revealing mistake: (Part 4) After Omega takes off his mask and looks in the mirror, when he sees that his physical body doesn't exist he puts his mask back on and screams, but when he shouts, "If I exist only by my will, then my will is to destroy," Omega's mask pops up off his face, and we can see the actor's blackened face as he shouts the last bit of his dialogue. (00:07:10)
Revealing mistake: When the Doctor and Jo see Bessie in the middle of the rocky area, there is the white chalky substance from the ground on her wheels, indicating she was driven to the spot rather than being "transported" to the black-hole.
Revealing mistake: In episode 3, when the second Doctor, the Brigadier and Benton emerge from the TARDIS, the doors are left completely open with the camera looking straight into them for a long time, revealing not only the emptiness of the police box shell, but also that there's a pair of secret doors on the opposite side to the entrance doors. These 'secret doors' come in handy during episode 4, allowing seven people to come out of the police box in the final confrontation with Omega. (Well, it is stated time and again that the TARDIS is "bigger on the inside than the outside". Now we know how that happens...).
Revealing mistake: At various times (especially in episodes 3 and 4) you can see actor Stephen Thorne's lips through Omega's mask (and in one profile shot you can also see his jaw), yet when his mask is removed, we find that Omega has been dissipated and has no face...
Revealing mistake: Whenever the TARDIS's scanner picture of the Doctor's laboratory is shown, the TARDIS itself is always in the picture.
Revealing mistake: Jo is hit by a rather large rock. Katy Manning visibly winces before it strikes (and bounces off lightly).
Revealing mistake: In episode 5, Codal discovers that what he thought was Taron is an invisible Spiridon. However, there is a glimpse of the actor inside the fur costume as he attacks Codal.
Revealing mistake: When Benton jumps over the maggots to get into the cave the Professor and Jo are hiding in, the jump causes the floor to move, giving away the fact that the floor is wood covered by a small amount of gravel.
Revealing mistake: In the finale, when Stevens is beating on the computer console, it moves around quite a bit, even thought it is supposed to be a strong and stationary object.
Revealing mistake: At the end of episode five, when James collapses against the wall, it wobbles under his weight.
Revealing mistake: Matte halos appear very frequently in this episode, particularly when descending into the mine shaft.
Revealing mistake: When Jo and the Doctor are rowing through the maggot lake, several times parts of the actor's arms disappear.
Revealing mistake: The explosion of Irongron's castle is obviously stock footage of a quarry explosion.
Revealing mistake: How did Rubeish's glasses manage to improve his chronic shortsightedness when they are obviously plain lenses?
Invasion of the Dinosaurs - S11-E2
Revealing mistake: At the beginning of episode two, the soldiers firing at the dinosaur are aiming up and well to the left of the creature.
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.
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