Conservative Party Conference, say, with stars (15)
I believe the answer is:
conventionalist
'with stars' is the definition.
The definition suggests a singular noun which matches the answer.
'conservative party conference' is the wordplay.
'conservative' becomes 'conventional' (similar in meaning).
'party conference' becomes 'ist' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'conventional'+'ist'='CONVENTIONALIST'
'say' is the link.
Can you help me to learn more?
(Another definition for conventionalist that I've seen is " rebel? Not at all".)