Bitter racist as horrible Conservative (9)
I believe the answer is:
sarcastic
'bitter' is the definition.
(thesaurus)
'racist as horrible conservative' is the wordplay.
'horrible' is an anagram indicator.
'conservative' becomes 'C' (UK political abbreviation).
'racist'+'as'='racistas'
'racistas' anagrammed gives 'sarcasti'.
'sarcasti'+'c'='SARCASTIC'
(Other definitions for sarcastic that I've seen before include "Pungent" , "Expressing ridicule, contempt, maybe irony" , "Bitingly ironic" , "Using mocking irony" , "Derisive" .)