According to Wikipedia, Mary's father was a surveyor and Nicholas' father was a GP. Nicholas was born in Grantham and Mary went to a school in Bath. There is no mention of them being brother and sister.
Thanks for that Wolf. I had an idea they were. Is there any evidence I can use to substantiate this as I want to add it to a quiz so have to be fairly sure of the facts?
There do seem to be a lot of references to them being siblings, as my sibling above has stated, but they may have all come from a single in-correct source.
They're not related at all .The only reason it was said they were is because they bear a passing resemblance to one another ( although I can't see it ) and this was put about as a joke in one of the Great British Bake Off blogs .