Hello Robert, I have just logged on for the first time and it's a bit late so apologies if this is a bit rushed.  I am a great granddaughter of Arthur Llewelyn Davies brother Maurice.  My mother has recently been writing about their family in fact I spent yesterday at Girton College copying more letters from Mary, Arthur's mother, to Arthur's sister Margaret.  I know from my mother's knowledge of Margaret (who lived with her at the end of her life when my mum was a girl) that as John Lleweln Davies their father prefered his second name he was known to them all as Llewelyn and they gave all the sons the name Llewelyn as a second name.which they chose to use as a double barrel surname.  Margaret was given a second name of Caroline I , but she was cross about this and chose to use the Llewelyn Davies as well.  My grandmother and her siblings all went on to be LD from then on so it would have been bizarre for Sylvia to revert to Davies when the whole family had adopted it, Emma Dogliani