I have traced my grandfathers family now.
He was in fact born Ernest Edwin Townsend. My mum remembered that she visited an aunt of my dads but had no name for her, the Aunt had a daughter called Geraldine so I worked back from there and found her mother Irene EE Townsend who was Ernests sister born after the 1911 census was taken.
The camberwell Helena Maud Green (Daughter of Arthur and Alice) is not my grandmother. I found the niece (living) of this Helena and spoke with her via Email, she told me that her Aunt married Freddie Woodnutt in 1916.
So now I am really stuck, I have no births to go on at all and I can't be sure if the marriage certificate I have is actually them although he does fit very well apart from the middle name of Edward but he is also Ernest Edward on my dads birth cert. This chap didn't seem to like any of the names his parents gave him
It may be that Helena was indeed French after all, and maybe went back to France which could be a reason for my dad never knowing her. We tried to work out when she left and think it was around 1925.
Can anyone give me an idea of where I should be looking next to find my Grandmother please.