Half-hearted Liberal member going round posh gardens (8)
I believe the answer is:
lukewarm
'half-hearted' is the definition.
('lukewarm' can be a synonym of 'half-hearted')
'liberal member going round posh gardens' is the wordplay.
'liberal' becomes 'l' (abbreviation).
'member' becomes 'arm' (arm is a kind of member).
'going round' is an insertion indicator.
'posh' becomes 'u' (abbreviation for upper-class - opposite to non-u).
'gardens' becomes 'kew' (Kew Gardens in London).
'l'+'arm'='larm'
'u'+'kew'='ukew'
'larm' enclosing 'ukew' is 'LUKEWARM'.
(Other definitions for lukewarm that I've seen before include "Indifferent" , "Somewhat cooler!" , "Half-hearted" , "Not enthusiastic, neither hot nor cold" , "Not having high temperature" .)