Moderate party committee backing secret meeting, we hear (8)
I believe the answer is:
centrist
'moderate' is the definition.
(I know that moderate can be written as centrist)
'party committee backing secret meeting we hear' is the wordplay.
'party committee' becomes 'NEC' (eg the Labour Party's National Executive Committee).
'backing' says the letters should be written backwards.
'secret meeting' becomes 'tryst' (tryst can mean a secret meeting between lovers).
'we hear' indicates a 'sounds like' (homophone) clue.
'tryst' is a homophone of 'trist'.
'nec' reversed gives 'cen'.
'cen'+'trist'='CENTRIST'
(Other definitions for centrist that I've seen before include "Politician who takes middle-of-the-road position" , "A middle-of-the-road person in politics" , "Moderate politician" , "Person who takes a middle-of-the-road political position" , "One taking the middle ground" .)