I've just had a thought which is a long shot as Rose Elizabeth Ellen Day (Herbert's older sister) has 40 Dartmouth Road as the address on her death certificate (William, her husband, was the informant).
I know that Rose was very family orientated as she was the informant for the deaths of her father, her older brother Henry and her younger brother Robert (my great grandfather).
Rose died in 1931 but William lived on for another 4 years if I am correct so it may be possible that Herbert was living with them.
As I said, it's a long shot but you never know!
Also, looking at Herbert & Lilian's marriage certificate from 1934, Herbert was living at 26 King George Avenue and Lilian was living at 20 Argyle Road. Both roads are in the Custom House area.