Other mistake: Pilot episode Mr. Lucas is holding the mannequin together with Miss Brahms. Mr. Grainger walks by and is appalled by the state of undress of the figure and says "Well, it's hardly sufficient, is it?" You can see the camera getting randomly out of focus in a bad, noticeable way. (00:03:20)
Other mistake: When Mrs. Brahms is talking to Mr. Granger, Wendy Richards' voice cracks stifling laughter when she says "Mrs. Slocombe didn't like to take down your trousers without asking you first." (00:18:00)
Camping In - S1-E4
Other mistake: The episode takes place on March 2nd, 1973 (date of the newspaper shown by Mr. Mash), but in Mr. Rumbold's office the sale chart for the month of March is already fully filled up.
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.