With regards to Elwyn’s biological father it’s highly unlikely that he is listed on his birth certificate. It will be blank. It’s a very recent thing for unmarried mothers to name the child’s father. One of my uncle’s was illegitimate and always wanted to know who his father was, but his mother would never tell him, and that was despite the fact that she was illegitimate, and you might have thought she would have understood the need to know. I think her view was “don’t talk about it, just get on with life”.
If you put the name Elwyn Dyer into “search all records” on Findmypast you will find no births, but you will find 2 marriages; one in 1956 in Eton, Buckinghamshire, and another in 1987 in Slough, Buckinghamshire. You will also find him on various Electoral rolls, so he might still be in Slough.