Continuity mistake: In the Marriage Counselor sketch, Deidre Pewty is wearing such a tiny miniskirt that when she sits we see she is wearing white knickers. When she undresses behind the screen she throws a pair of black knickers out.
Oh, You're No Fun Anymore - S1-E7
Continuity mistake: During the science fiction sketch, when Eric Idle is reporting his blancmange sighting to John Cleese the clock in the background jumps backwards a few minutes.
Man's Crisis of Identity in the Latter Half of the Twentieth Century - S1-E5
Continuity mistake: At the start of the interview sketch, and at several times throughout, Cleese says he's interviewing people for a management training course. At the end, however, he suddenly claims it was a job interview.
Continuity mistake: At the beginning of the 'Ministry of Silly Walks' sketch, John Cleese is holding his briefcase in his left hand. when the shot changes to outside, showing him leave the newsagents, it switches to his right.
Mr. & Mrs. Brian Norris' Ford Popular - S3-E2
Continuity mistake: When Mr. Norris sets out on his expedition, it is April 24. But when we see his diary, the day is the 24th, but the month (on the top of the page) says "October."
Continuity mistake: At the beginning of the vegetarian restaurant sketch, Eric Idle stands right behind the pointy sculpture. It is quite short and in some shots the points of it are visible right at the bottom of the screen, but in other shots people stand and walk through right where it is meant to be. And in the final shot, when Eric is complaining about the punchline, it is definitely gone.
Continuity mistake: During the Ministry of Silly Walks sketch, in the office, John Cleese pulls out a film-projector from his desk, and you can see the power cord plugged into the back of it. After the spoof black-and-white film footage showing the silly walks, John Cleese throws the projector away. The power cord, which was originally plugged in, has disappeared completely.
Continuity mistake: We are told that the Germans develop and broadcast the "V-Joke" in 1944, but when we cut to Terry Jones and Graham Chapman listening to their radio and hearing the joke, the caption reads "1942...Somewhere in England".
Salad Days - S3-E7
Continuity mistake: In the 'Sam Peckinpah's Salad Days' sketch in Series 3, Show 7, the scene suddenly changes from a bright sunny day to a pitch black night - this was apparently due to technical delays, but the effect makes it look like an extension of the 'pretentious director' parody.
Chosen answer: The song you talk of was originally a poem by William Blake called 'Jerusalem'. It speaks of the possibility of Jesus having visited England. The poem has four verses but you only ever hear the Monty Python boys sing the first one which goes, "And did those feet in ancient time/Walk upon England's mountains green/And was the holy Lamb of God/On England's pleasant pastures seen?" If there's any sort of in-joke connected to it's use, I'm not aware of it. It seemed to just be the standard song/hymn they used when a song was needed that wasn't sketch specific. Some of the sketches it appeared in were 'Salvation Fuzz/Church Police', 'Buying a Bed' and 'The Art Gallery Sketch'. Something that may be relevant, though, is that the only one who was present every time it was sung was Eric Idle. Perhaps he just liked it?