Advantage of Cockney’s row of bushes (4)
I believe the answer is:
edge
This clue is a double definition.
'advantage' is the first definition.
(having the edge is having an advantage)
'cockney's row of bushes' is the second definition.
('hedge' - I've seen this before - said with the 'H' dropped - a cockney accent.)
'of' is the link.
(Other definitions for edge that I've seen before include "Bite" , "Demarcation" , "Periphery" , "Intense quality; limit" , "Create borders" .)