As with the later in life, John William who died in the USA, the time period 1947 to 1952 is not a period area we are use to helping with, as most family researchers usually manage to get back to the 1911c with their own family knowledge gained from their family and BMD certs.
Just a couple of examples,
WW1 and WW2 also easier travel in the 20th century, people moved around more. Troops brought over in Europe WW1 and WW2 from the commonwealth countries and the USA, or say a man doing service repair for a international company working in England met a lass, they married, he stayed here as did a few USA troops in WW2.
To the far extreme -
Say he was the son of a big time well known named published criminal or murder or William was a bigamist -answer:- He changed his name.
https://www.gov.uk/change-name-deed-poll/overviewThere are endless possibilities.