Hello mum mum,
As you don't mention a name for your cousin's uncle, I thought I'd post what I think are his details as there may be others who can help.
I've found the marriage details:
Edna Sambrook (note the spelling) to Samuel Morris or Goldbaum
September quarter 1945, Eton district GRO ref 3a 4586
And the birth of their son:
John A Morris, September quarter 1946, Windsor district, GRO ref 6a 330 (mothers maiden name Sambrook)
A possible entry for Edna's birth:
Edna L Sambrook, December quarter 1922, Medway district, GRO ref 2a 1158 (mothers maiden name Barnard).
and her brother:
Jack C Sambrook, June quarter 1920, Medway district, GRO ref 2a 1592 (mothers maiden name Barnard)
Researching the Sambrook family may be easier, and any living descendants may point you in the direction of Edna's son.
I'm sorry that I can't help any more, but good luck with your search.
Carol.