Revealing mistake: UFO - Timelash - in this episode the aliens with the help of 'turncoat' Turner have frozen a moment in time in which they will attack and destroy SHADO HQ. Everything and everyone is frozen in place - except for the guy in the background walking across the road during Straker's and Turner's 'car' chase in the 'Harlington/Straker' go carts.
Revealing mistake: "Computer Affair": In the interior shots of Mobile 1's cockpit, we see that there's a crew of 3 and that the pilot is black. But in shots of the exterior (miniature model stock footage), there's only one occupant, a pilot, and it's a doll with distinctively Caucasian features.
Continuity mistake: A UFO crash lands in Canada and sits amidst trees in a wooded area. Just before the craft explodes, the only snow visible is on mountains in the distant background. After it explodes, however, the ground and trees all around it are suddenly covered with snow.