I'm guessing you've already checked to see if there are any records of children admitted to the Watford Children's home. These records if they exist would probably be at the local archives. Not sure if it's the correct home, but looking at Hertfordshire Archives catalogue, they have some records for Ashby Road Children's Home, 1903-1955 (HSS8/16).
The birth date might have been 'invented' by the home, if nobody knew when he was born.
As Cyril Lewis might not even have been his birth name, I think DNA may be key here to narrow this down. Unfortunately it doesn't sound like any of the matches are that closely related.
You could look into Cyril's son doing a Y-DNA test. Y-DNA is passed only father-to-son, so this could help to narrow down whether he is related to other Lewises or should you be looking into other surnames. FamilyTreeDNA has the largest Y-DNA database, so testing with them is best. A 37 marker test is usually sufficient to screen for possible matches, you can always upgrade to higher level testing if needed. But it is very much luck of the draw whether there are any useful matches or not.
If there are any close male matches on Ancestry it might be worth trying to convince them to take a Y-DNA test as well, to work out if you are related on the paternal line.
Alexander