During the series, Emmet and others are seen being frightened by Hyacinth's singing voice. In reality, Patricia Routledge is known for her powerful singing voice and has a long career in musical theatre.
The FH on Onslow's hat stands for Fulton Hogan Ltd., a New Zealand asphalt and road-building company. When Geoffrey Hughes was there promoting a show, he was given that hat by one of the company's lorry drivers.
In one episode Onslow and Daisy are in bed reading, conversing about DIY, when Onslow describes himself as being more intellectually than manually gifted. During this time he is glancing at a hardback book, the title of which is difficult to see on screen. The book is a newish copy of "Principles of Condensed Matter Physics."
Ironically, while Hyacinth brags to Elizabeth that Violet has a swimming pool at her house, the house, used as Elizabeth's in the show, actually has its own. This, of course, was never featured onscreen.
Onslow's often seen, beat up car is a 1978 Ford Cortina (Number plate: VSD 389S). A running gag throughout the series is the car backfiring loudly upon arriving and leaving a destination. For visual and comedic effect, a small amount of gunpowder and a charge were put in the exhaust pipe causing a large puff of smoke and sparks.