You bugger, I live in Norfolk!
(Though I'm from county Durham where we were crossed with pit ponies....*grins*)
The problem with genetics isn't really the issue here though is it?
These two, twins split up at birth, were total strangers and in this day and age, with multiple marriages, adoptions, test tube babies, I wonder how many are really undiscovered.
Of course, the logic dictates that if it is two half siblings either one or the other parent would know, but what of the mother who gives up a child for adoption, marries then has other children.
The children don't always know they are adopted and the parent/s don't always know what has happened to the children they had adopted.