Visible crew/equipment: Episode 5, while Zoe and Jamie are at the Weather Control Station, when they hear the Ice Warrior approaching they both hide, and the actor's T-mark is visible on the floor. (00:18:00)
Revealing mistake: When Slaar discovers the video link is operational and being viewed on Earth, in the closeups of Slaar we can see the edge of the reptilian mask and the actor's real human neck. (00:20:40)
Continuity mistake: Patrick Troughton's sideburns keep appearing and disappearing, depending on whether what is being shown is location filming or studio.
Revealing mistake: When Jamie is wrestling with one of The Ice Warriors in a storage room, one of them gives the wall an almighty knock and it nearly falls down.
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