Impropriety of only Conservative ideology (8)
I believe the answer is:
solecism
'impropriety' is the definition.
(thesaurus)
'only conservative ideology' is the wordplay.
'only' becomes 'sole' (synonyms).
'conservative' becomes 'C' (UK political abbreviation).
'ideology' becomes 'ism' (capitalism, communism etc).
'sole'+'c'+'ism'='SOLECISM'
'of' is the link.
(Other definitions for solecism that I've seen before include "A mistake in the use of language" , "Absurd or mistaken word or act" , "Grammatical mistake" , "Social gaffe" , "Faux pas" .)