Dressed down in the past, Conservative kept out of sight (7)
I believe the answer is:
chidden
'dressed down in the past' is the definition.
(historical past tense form of 'chide')
'conservative kept out of sight' is the wordplay.
'conservative' becomes 'c' (abbreviation commonly used in UK politics).
'kept out of sight' becomes 'hidden'.
'c'+'hidden'='CHIDDEN'
(Other definitions for chidden that I've seen before include "Ticked off" , "carpeted" , "having been told off earlier?" .)