Continuity mistake: At the end of the show, after they reveal the 'new' ladies department. Mr Grainger is not wearing his glasses, as Mrs Slocombe has them in her purse, the shot changes to Mrs Slocombe, then back to Mr Grainger he is wearing his glasses, and there is no way he could have got them from Mrs Slocombe.
Continuity mistake: Mr. Lucas says the figures for the previous Monday were 325 pounds, and at that point in the day the departments combined (170 and 150) were up to 320, five pounds short. However, later when Mr. Rumbold is talking to Mr. Grace about the sudden drop in sales, he says they are "still 20 pounds short" of the previous Monday.
Continuity mistake: Mrs Slocombe arrives with her hair in disarray, but once she walks away she only has time to put her coat away before she returns, by that time her hair is neat with no evidence of it being messy. She had to have returned quickly to hear Mr Humphries' story as she comments on it shortly after.
Revealing mistake: The cake the groom's father has is treated as if its real, but when smashed over Mr. Grainger's head it's obviously Styrofoam and hollow.
The Father Christmas Affair - S4-E7
Revealing mistake: At the end, when Mr. Grace is inspecting the Father Christmases, you can see his secretary behind the scenery waiting for her cue.
The Father Christmas Affair - S4-E7
Visible crew/equipment: When Mr Humprhries is talking about the whereabouts of Mr Grainger, explaining about the inability to remove the Al Jolson make up, you can see John Inman looking up before having his face shadowed by a boom mike.
Factual error: Mrs Slocombe's cat gives birth, but the kittens shown at the end are way older than ones who are supposed to have been born just moments before.
A Change Is as Good as a Rest - S5-E2
Visible crew/equipment: In the opening scene in the board room when Mr. Lucas is commenting on how Mrs. Slocombe is "big in the south," you can see the shadow of a boom mike floating back and forth across the table.
Continuity mistake: In this episode, it is revealed that Mr. Lucas' first name is Dick; but way back in series 2 ("The Clock"), his first name is given as "James." This discrepancy takes place a few times over the course of the entire show run.
Revealing mistake: When Captain Peacock goes behind the curtain to the hall way to Mr Rumbold's office, you can see that the sets are right next to each other and the other actors are waiting in there for the next scene.
Revealing mistake: When Mr. Lucas gives Mrs. Slocombe the radio mike, it slips down her dress out of reach; Mr. Harman says "It can't have gone down all that far," and he's right: The short cord of the mike is visible sticking out of the dress for quite some time until Mrs. Slocombe herself pushes the mike down (in the appearance of trying to fish it out).
Other mistake: After Mr. Tebbs finishes telling his story about selling seven toilets in one day, Mr. Lucas makes a wisecrack and Mr. Humphries says "I think it's the way Mr. Tebb [instead of 'Tebbs'] tells it."
Continuity mistake: Normally the windows in Mr Rumbold's office are latch swing open style, but when the staff are viewing the parade they are plainer push up windows.
Revealing mistake: During the end credits of this episode, a bowl of soup is shown. A frog appears in it for a few seconds and then sinks under the water again. You can see the string being used to pull the frog up. It surfaces as the frog does, and is very easy to spot.
The Punch and Judy Affair - S7-E8
Revealing mistake: When Mr. Humphries complains that the sauce is stuck in the ketchup bottle, one can see the silver plastic seal keeping it in, not some mysterious clog.
The Punch and Judy Affair - S7-E8
Revealing mistake: When the staff are assembled in Mr. Rumbold's office sans Mr. Lucas, Lucas comes rushing in late. However, before he does you can see him standing just outside the door, waiting for his cue to rush in.
Continuity mistake: In the ruined photo taken of Old Mr. Grace and his nurse and secretary, the secretary is looking away from the camera and her leg is raised. However, in the scene preceding, she was looking at the camera and raised her leg after the flash went off. Also in the photo, both of Mr. Humphries' feet are in the air, though one was on the floor when the picture was taken.
Revealing mistake: At the beginning of the Scottish dance when Captain Peacock is demonstrating the sharpness of the swords, he first cuts through the center of a newspaper page held up by Mr. Spooner. However, you can see that, just before the sword makes contact, Spooner actually tears the paper apart down the middle.
Goodbye Mrs. Slocombe - S10-E1
Other mistake: When Mr. Humphries first comes back to the department in drag and talks to Capt. Peacock before being directed to the Ladies Dept., you can see, in the background, Mr. Spooner trying desperately (and unsuccessfully) not to laugh.
Goodbye Mrs. Slocombe - S10-E1
Audio problem: At the end when Capt. Peacock comes onto the floor in his maintenance garb, Mr. Harman points him to a spot on the floor and tells him to mop it up. In the initial shot Harman is indeed telling him, but when the camera cuts to another angle Harman is visible and still talking but his lips aren't moving.
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.