Regarding Brummie accents, I was told some time ago that the Brummie accent is the true English accent as spoken in the times of Henry VIII and Liz I, especially amongst the gentry
At some later time during the reign of Charles II I believe, eating plums became became fashionable and thats how we have the way Liz II speaks. So don't run Brummie Williams accent down too much.
It may have a very aristocratic pedigree.