Many thanks to all of you who have posted replies, you have been a great help. I think I'll have to keep searching the Census for a local McGill and hope one may be the right father.
Hi rachelm700
Nae prob!
This is a perfect example of the different routes to the same solution!
Gadget got there via the 1881 census entry; whereas I reached the same conclusion via the 1906 marriage entry, the names of the parents, their date of marriage, linked to the most probable birth record for Williamina, implying a date of birth earlier than that of the parents shown in the 1906 marriage; thereby implying the possibility of an illegitimate birth, so that I went looking for a Williamina ROGERSON or KENNEDY born in the right year and location !! ..............
ibi