I think Dora (his possible mother) may have been Agns Dora Booker.. but it doesn't look like she was married.
I may come back to you... 
There is an
Agnes Dora Booker born in c1884 Southampton her parents are
Charles & Susan (1891c) in 1901 she's just Dora Booker and a servant, I think this Agnes Dora Booker
can be ruled out , she died 1944
Agnes Dora Booker spinster of Arrow Lawn Eardisland Leominster died
2 June 1944 Admin to
Henry Hardy Booker retired civil servant
(if you look at the 1891 census you will see that Henry Hardy is her brother)
Henry Hardy Booker 37 Salisbury Rd Highfield Southampton died 4 June 1954
Probate to Lloyds Bank
You would need to check
Albert Hampshire Booker's birth certificate (birth reg. given by Suz) to be certain of his mother's name and if she wasn't married hopefully his father's name might be mentioned - you know his grandparents are named Rueben & Mary
That would then confirm if the Dec 1911 marriage might be the same couple (ie Albert Hampshire Booker's parents)