Support part of UK backing Asian republic (5)
I believe the answer is:
india
'asian republic' is the definition.
(I've seen this before)
'support part of uk backing' is the wordplay.
'support' becomes 'aid' (to aid is to help or support).
'part of uk' becomes 'NI' (Northern Ireland).
'backing' shows that the letters should be reversed in order.
'aid'+'ni'='aidni'
'aidni' reversed gives 'INDIA'.
(Other definitions for india that I've seen before include "Large Asian republic" , "Cricket team" , "Second-most populous country" , "New Delhi is its capital" , "Type of paper, rubber etc" .)