I can confirm Burl's posting about the saying being common on the Notts/Derbys border and the pronunciation of "mother". And it were always "black" ovver theer. I suppose we're including DH Lawrence country here and I used to hear it all the time in Eastwood, along wi' a lot of theein' and thaain' me duck.

I wish I could remember more of my maternal grandparents' local pronunciation (Beeston/Long Eaton)- I do remember my grandma pronouncing the city of Derby like the US hat rather than "Darby".