I didn't watch it but I noticed earlier that the Radio Times website described Kerry Howard's performance as a "charmingly faithful tribute to Patricia Routledge’s character". It was Roy Clarke's script that the writer felt lacked lustre:
http://www.radiotimes.com/tv-programme/e/fbv2xp/keeping-up-appearances--young-hyacinth
The idea of her coming from a poor background, but then gaining social pretensions through working as a maid, certainly rang true for me though. My mother was born into a working class family in what was then the poorest borough in the country. (Limehouse, London). However she went 'into service' with a Harley Street surgeon and, from then on, everything in her life had to be done "as it was in the big house".
Despite the fact that I was brought up on a council estate, in a house where there was little money for heating, etc, my mother made it very clear that I should always look down on "poor people" (it never occurred to me that we were actually 'poor people'!) and, far more importantly, upon "common people". She had a 'telephone voice' which Roy Clarke could have used to base Hyacinth Bucket's "the lady of the house speaking" line upon, despite the fact that she could only use it after she'd fed her 4d into the slot in the phone box across the road from our house.