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.