I chatter excitedly about Conservative mastermind (9)
I believe the answer is:
architect
'mastermind' is the definition.
(thesaurus)
'i chatter excitedly about conservative' is the wordplay.
'excitedly' indicates an anagram.
'about' indicates putting letters inside.
'conservative' becomes 'c' (abbreviation commonly used in UK politics).
'i'+'chatter'='ichatter'
'ichatter' with letters rearranged gives 'architet'.
'architet' going around 'c' is 'ARCHITECT'.
(Other definitions for architect that I've seen before include "professional" , "Building designer" , "Wren perhaps" , "Perhaps Scott" , "Author" .)