I am prepared to preemptively call this the best Carry On of the 1970s. It's a damn sight better than Up the Jungle, Loving, and even Henry (which I mostly rewatched recently despite not reviewing it here). Ironically enough there's something of a throwback early '60s feel to it, owing in large part to Sid James playing a sort of straight family role, plus the almost "kitchen-sink drama" element that keeps threating to come out. Yet it's also very much a time capsule of early '70s Britain - the sexual attitudes, the union politics, the home décor right down to the ugly wallpaper.
Basically this film is kind of sad, like so many later Carry Ons - but, in this case, the sadness does not play as entirely unintentional. Instead it manages to work in the movie's favor.