Revealing mistake: The bottle of acid that the Doctor throws at Mestor breaks open well before it hits the shield that Mestor is projecting around himself.
The Tomb of the Cybermen - S5-E1
Revealing mistake: When Jamie and the Doctor try to open the doors to the tomb, watch them push it with their feet.
The Tomb of the Cybermen - S5-E1
Factual error: When the group divide up into parties, the leader says they need to be at the rocket at 1630, so meet here at 1625. He then goes on to say that will give them an hour to look for anyone that's missing. The other actors seem to notice his mistake because they either look puzzled or look off camera, probably seeing if anyone would shout "Cut."
Genesis of the Daleks - S12-E4
Revealing mistake: During the Doctor's early conversation with the Time Lord, there is fog swirling around them. When the Doctor agrees to take on the mission, it suddenly appears very concentrated around the tip of the rocks behind them, as if generated from a source behind the rocks. Normal fog would not do this, and it's clear that dry ice was used as the fog effect (DVD commentary confirms this). (00:02:45)
Revealing mistake: The knife that Leela kills Meeker with is very obviously loosely attached to his clothes. It wobbles back and forth after he falls.
The Caves of Androzani - S21-E6
Revealing mistake: In the very first shot of Morgus' hand-held computer, it's obvious it's a TV remote. Look for the controls for contrast and tint.
Continuity mistake: From time to time in episode four, the "frozen" robots on the command deck can be seen to wobble - the most noticeable is when SV7 is threatening Uvanov over the communicator.
The Monster of Peladon - S11-E4
Continuity mistake: In episode three, Eckersley turns on the security monitor. The very first image is of the entrance to the refinery, but it does not show the Doctor and Gebek trying to break in. Eckersley then flips through the images and finds one of the refinery with the Doctor and Gebek breaking in.
Visible crew/equipment: In episode one, when a Voord falls through a pyramid door, a stage hand can be briefly seen on the other side.
Audio problem: When the Doctor arrives at UNIT HQ in his stolen car, he speaks to a guard. We see close ups of the guard twice...but watch the brief clip of the Doctor (Jon Pertwee) between the two and you can just see that his lips aren't moving even remotely in synch with the words. (In fact, it is just a repeat of the previous shot of the Doctor, with new lines dubbed in).
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.
Factual error: The Doctor states that the radio waves take two minutes to get from Mars to Earth. The time interval can vary dramatically depending on where the two planets are in their orbit. But at absolute closest approach, Mars is just over three light minutes from Earth.
Factual error: When Kathleen's baby Audrey is revealed for the first time, the baby is clutching a "SuperTed" teddy bear (circa 1984). The story is supposed to be set in 1943...
Continuity mistake: When the Count's henchmen come into the café to get the Doctor, Romana and Duggan, they usher them all out at gunpoint. When you see them in the location filming in Paris, Duggan's not there...but back at the Count's place (in the studio in London) he's reappeared.
The Power of the Daleks - S4-E3
Revealing mistake: The Daleks that appear in this and other Doctor Who stories were rather expensive, so some ingenuity was required to make the small number available look like they were more than they were. Tricks employed in "The Power of the Daleks" included making four Daleks look like an army by having them circle around the set a few times (note the delay between the fourth Dalek exiting and the "fifth" Dalek entering), and the blatant use of photographic blow-ups in place of "real" Daleks.
Continuity mistake: The end of episode 7 does not match the reprise of the story at the start of episode 8. The Doctor, Security Chief and guards file into the SIDRAT in a different order.
The Tomb of the Cybermen - S5-E1
Revealing mistake: During the fight scene between Toberman and the Cybercontroller, the Cybercontroller uses a very visible harness to lift Toberman over his head, and the wires attached to the harness Toberman is wearing are also very visible. When Toberman, in return, lifts the Cybercontroller above HIS head, it is obvious that what Toberman is lifting is an empty costume, with no-one inside it.
Revealing mistake: When the robotic Doctor first appears - and in many of the later scenes involving the jungle on Mechanus - it is very obviously not William Hartnell playing him, but a vaguely similar double. In addition, his lines have been dubbed by Hartnell and do not always match the movements of his mouth.
Planet of the Spiders - S11-E5
Revealing mistake: In episode three, when Tommy peers into the room where the Doctor and Sarah are talking to Cho-Je, the camera moves forward - and bumps into a wall with an audible thud and noticeable jerk.
Continuity mistake: At the beginning of the third episode, the countdown reads 49:18:32 in the close up, but when the Brigadier walks across the room it now is on 49:15:01. (In other words three minutes thirty one seconds have elapsed). Yet these two events are about ten seconds apart. Also, the timer should never read either of these times. The professor moved the countdown forward to exactly 49 hours (49:00:00).
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