Revealing mistake: When Mr. Lucas goes to "knee" the pair of pants, the pants already have the hole in them, and his knee doesn't rip anything.
Camping In - S1-E4
Revealing mistake: Mrs. Slocombe enters her tent after telling Captain Peacock about the top window. Peacock then obviously uses that moment to stand on his tiptoes and peek in. You can see to the right of the tent the metal cart pushed by Larry Martyn discreetly peek out of the stage entrance and stop as he waits his cue to come on the set, to a rumbling noise. (00:13:35)
His and Hers - S1-E5
Revealing mistake: On the tape player that the sales girl is using, the reels are moving in opposite directions, the tape can't play doing that.
Answer: That wasn't possible in 1972. Until recently squatting was a civil offence in the UK, not a criminal one, and removing squatters was a complex and time consuming business.