Reportedly, Cockney bloke spotted Jacob's brother (4)
I believe the answer is:
esau
'jacob's brother' is the definition.
(I've seen this before)
I don't understand how the remainder of the clue works.
(Other definitions for esau that I've seen before include "Brother to Jacob (OT)" , "Isaac's hairy son" , "First son of Isaac (Bible)" , "Isaac's eldest son" , "Hairy brother to Jacob in Bible" .)