Be successful going round Hungary for gorse (4)
I believe the answer is:
whin
'gorse' is the definition.
('whin' can be a synonym of 'gorse')
'be successful going round hungary' is the wordplay.
'be successful' becomes 'win' (I've seen this before).
'going round' is an insertion indicator.
'hungary' becomes 'h'.
'win' enclosing 'h' is 'WHIN'.
'for' is the link.
(Other definitions for whin that I've seen before include "Hard rock" , "Gorse, furze" , "prickly shrub" , "Prickly plant" .)