Thank you for taking the time to reply Shane. I will have a look at the link you put in your reply and then see what I can find out from the BMD indexes. I'm a bit nervous about ordering certificates from Ireland, only ever done it once before and still quite unsure what I'm doing! Also great idea about checking out the census for Blacksmiths, will do that too.
I have no information about Florence at all, only that I'm told she is supposed to have come over from Ireland with her mother. She was my dad's much older half sister who disappeared off the scene before he was old enough to know her well.
I have had a look in the English 1911 census for an Annie/Mary Ann Martin and there is only one Mary Ann Martin with a daughter Florence, living in Greenwich, London, but she is too old and has quite a few other sons, so this can't be my woman. Another Annie Martin in Greenwich is the right age, a domestic servant, but born in Yorkshire and has no daughter Florence.
In the Irish census I've found three Mary/Annie Martins in Cork, aged between 26 and 29, all married but no Florence, and one has three sons, so I don't think that could be her. I suppose the other two may be possibles, one is in Foherlagh and the other Coolmain - but these areas mean nothing to me unfortuantely, don't know if they would be near Bluepool, Kanturk? And I've found a Mary Courtney, age 24, boarder, in Gortnatubbrid. As I have so little to go on it all seems a little overwhelming I must say.
Just as an aside, I see from the bottom of your post you are interested in Sheridans in Dublin, my grandfather was a Sheridan from Dublin, another needle in a haystack I've done better with than I thought I'd ever do with the help of Rootschatters.
Many thanks again for your suggestions and taking the time.
PollyB