Re: "Erm" is for the speech impedimented.
" I think it was most widespread in the remote south east of the country - [...]"
Standard pronunciation of "erm" in my northern working class childhood. The R lengthens the sound to indicate the speaker is cogitating before making a chosen statement about something.
Our 1960s secondary school English teacher had two language triggers. A kindness on his part was in trying to eradicate our local pronunciation of short vowels and some overstressed endings.
His real hatred was reserved for Americanisms. You learned to duck if one of the latter inadvertently escaped your lips. Even at a reunion 45 years later - old boys were careful to say "round" rather than "around".
Biting the hand that feeds IT
