I'm currently dialect coaching an LA production of Roald Dahl's classic The BFG. The first thing I have to say is that when I found out this had been adapted for the stage, I was pretty excited--The BFG was always a favorite.
But now on to the matter at hand… There's a scene with the Queen of England and Mary, her maid. Mary repeatedly addresses the Queen as "ma'am." After some research, I quickly learned that "ma'am" should rhyme with HAM, not TOM. Take a look at this:
It's ma'am as in ham, not ma'am as in farm. Lower class people, or domestic servants would say "mum" when referring to their employers, but that hasn't been the case for about 100 years. I suppose some regional accents could pronounce "ma'am" as "mum" but I'm struggling to think which. Cockney, perhaps. These days, mum is what we call our mothers. It's not got anything to do with the Queen.
I must admit that I heard Helena Bonham Carter say this first in the movie The King's Speech. Always good to find confirmation!
The BFG by Roald Dahl
adapted for the stage by David Wood
Accents: British (RP, Posh, Estuary/Working Class, Swedish)