Thanks Sue, these are indeed possibilities to be considered.
My Dad's sister however, as far as I know, was Frances Marion Christian Shimmin, so the given names would not tie up.
Secondly, an informant from Canada, who started this part of the search said that the marriage to Mr. Clarke bore no children, this too has to be "proved", I know, but no children have ever been mentioned.
Thanks for the ideas, I will follow them up.Colin.