Jean, You said earlier that Harold had tried to keep in touch with his son by writing. Are there no clues as to where he was and what he was doing in the letters? When was the last letter written?
There are several Harold G marriages in England and Wales after 1948, but without buying all the certs and checking the age of the groom, his father's name and his occupation (at £9 + each) you wouldn't know if one was even possibly your man. In addition, he may have married overseas or in Scotland - different sets of records.
If it was my problem, I would start by noting down every single fact known about Harold. Then I would research Harold's birth and his parents. Try to find his birth cert and then his parent's marriage cert. Try to find out when Frederick died, where is he buried, did he leave a will, is Harold mentioned in it, where is Frederick buried, is Harold buried with him, what about Harold's mother, when and where did she die, is Harold buried with her, did Harold have siblings, one may have had an unusual name and be easier to trace and so on. You won't find a web-site with all the info on and this quest will involve a lot of detective work and probably some expense.
It is notoriously difficult to track people in 20th century because 1911 census is the last one available and people's mobility was so much greater after 2 world wars. There is a remote chance that a letter to the local Lewisham newspaper may produce some clues
