One of nine films Kathleen Harrison appeared in with Stanley Holloway and one of seven she appeared in with Dandy Nichols.
Ada uses a "planchette" to contact the spirit world. Americans know this as a Ouija board. The word "planchette" refers to the (usually) heart-shaped mover, though Ada uses a glass.
This is the second time that happens the siege of some common people against the Crown. The other time was in PASSPORT TO PIMLICO 1949, in both films featuring Stanley Holloway and Naughton Wayne.
Before the battle Henry Lord had an argument with Mr. Filch, he said a four letter word to Mr. Filch but the word was covered be the noise of the drill.
Stanley Holloway was 2nd choice for the male lead.