Isolationist, cross, reversed plan for buying a single award (9)
I believe the answer is:
xenophobe
'isolationist' is the definition.
(a xenophobe might support isolationism)
'cross reversed plan for buying a single award' is the wordplay.
'cross' becomes 'x' (X is cross-shaped).
'reversed' is a reversal indicator.
'plan for buying' becomes 'HP' (hire purchase).
'a single' becomes 'one' (a single thing - only one).
'award' becomes 'OBE' (Order of the British Empire).
'hp'+'one'='hpone'
'hpone' in reverse letter order is 'enoph'.
'x'+'enoph'+'obe'='XENOPHOBE'
(Other definitions for xenophobe that I've seen before include "One fears or hates foreigners" , "a kind of racist?" , "Person fearing strangers" , "One who doesn't like foreigners" , "Hater of foreigners" .)