My Mother used to say, “it’s black over Bill’s Mother’s”. I questioned her as to why it was black, who Bill was and where precisely his Mother lived, but to no avail. She didn’t really enlighten me.

Julie Legg offered the following origins of the expression which are entirely believable. “Apparently it refers to Shakespeare and his mothers cottage as it was a midlands saying. Or refers to Wilhelm II and the threat from the east ( ie referred to bad weather coming from the east “.

The point being, it was a common Midlands or Brum saying, so the family would have been familiar with it, and your antecedents used it. My Mother also used to say “Well, I’ll go to the foot of our stairs” referring to something unbelievable.