Leading Conservative delivers post (7)
I believe the answer is:
upright
'post' is the definition.
(thesaurus)
'leading conservative' is the wordplay.
'leading' becomes 'up' ('up' can be similar in meaning to 'leading').
'conservative' becomes 'right' ('right' can be similar in meaning to 'conservative').
'up'+'right'='UPRIGHT'
'delivers' acts as a link.
(Other definitions for upright that I've seen before include "deserving respect" , "with principle" , "Standing vertically - post" , "Sort of piano" , "Honest like a vertical post" .)