Visible crew/equipment: In "The Desparate Hours", right at the end when Barraclough is in Fletcher's cell, when Fletcher says, "I never heard nothing" you can see the shadow of the boom mic on his face.
Continuity mistake: Just after Warren says "we want a riot," the canteen door is already open and the prison guard is seen going through it. A few seconds later the guard is seen again banging on the door to get out.
There was an American version of this classic UK show. It was titled On the Rocks. The script was reworked in order to make the style of humour suit the audience. It lasted one series before being cancelled in May '76.