Criticise one Conservative creating alarm (5)
I believe the answer is:
panic
'alarm' is the definition.
(thesaurus)
'criticise one conservative' is the wordplay.
'criticise' becomes 'pan' (informal term meaning to criticise heavily).
'one' becomes 'i' (Roman numeral).
'conservative' becomes 'c' (abbreviation commonly used in UK politics).
'pan'+'i'+'c'='PANIC'
'creating' is the link.
(Other definitions for panic that I've seen before include "Uncontrollable terror, infectious fear" , "Lose one's cool" , "Sudden alarm" , "Frantic fright" , "Frantic fear" .)