Conservative list is fair (5)
I believe the answer is:
clean
'fair' is the definition.
('clean' can be a synonym of 'fair')
'conservative list' is the wordplay.
'conservative' becomes 'c' (abbreviation commonly used in UK politics).
'list' becomes 'lean' (I've seen this before).
'c'+'lean'='CLEAN'
'is' acts as a link.
(Other definitions for clean that I've seen before include "Unspoiled" , "Untarnished" , "not spotted" , "Untainted" , "How confessor comes" .)