Deliberate mistake: Because Stephen Greif tore an Achilles tendon playing squash, a stand-in had to complete his scene with Servalan in Ensor's underground complex. The result was a very odd segment in which we hear Travis' voice (pre-recorded by Greif) answering Servalan's lines, but never see him - except for an awkward shot of shuffling, black-booted feet that are all-too-obviously not Greif's.
Blake's 7 (1978)
1 deliberate mistake in Orac
Starring: Jan Chappell, Michael Keating, Paul Darrow, Peter Tuddenham
Time Squad - S1-E4
Continuity mistake: During Blake's first encounter with Cally, the smudges on the front of his tunic (including a big chalky footprint left by her boot) disappear, reappear and rearrange themselves several times between shots. (00:31:20)
Trivia: The box-like entrances to the underground lair proved problematic for the Space Rat actors. When several of them were supposed to spill out on cue, the box walls and their heavy helmets prevented them from hearing the director, who repeatedly screamed "Action!" to no avail. A lone voice from inside the box eventually shouted back, "Can't hear you!"