Thanks to both of you, Christopher & Mary
I know of Michael & Mary's children - Owen was my Grandfather - and of all the other members of the family latterly. It was M & M's roots that I can find no trace of.
Since posting my original topic, though, I have found out that Michael had a brother, William. What I know is as follows:-
The first record I have is a Birth Certificate of a girl, Margaret, born on 19th January 1871 in Greenhill, Shotts, Lanark, Scotland. Parents are registered as William Biggins ( Drawer in Iron Pit ) and Elisabeth Winterson. Marriage is said to be " 1860(?) December, NewtonButler, County Fermanagh, Ireland ". William registered the birth with his mark - as had his brother Michael at the birth of his kids. William was killed in a mining accident by " falling among the machinery of a coal pit engine, died almost instantaneously " on 25th September 1871. Parents are confirmed as Bernard Biggins & Catherine Currie - apparently both still alive. Death was registered by his brother, Michael.
What is curious about the death certificate is that under name not only is William known as Biggins he is also stated to have the " alias Currie " ( ie his mother's maiden name ). An alias is something you would not normally broadcast (?) so why would it be on your death certificate?
So I now have Co Fermanagh as a possible origin for my GGFather - Nothing is ever simple in genealogy!!!!!!!!!
Malcolm