Conservative runs high-class vineyard (3)
I believe the answer is:
cru
'vineyard' is the definition.
(I've seen this before)
'conservative runs high-class' is the wordplay.
'conservative' becomes 'c' (abbreviation commonly used in UK politics).
'runs' becomes 'r' (cricket abbreviation).
'high class' becomes 'u'.
'c'+'r'+'u'='CRU'
(Other definitions for cru that I've seen before include "French vineyard (and the wine from it)" , "Superior vineyard" , "Source of wine" , "Grounds for eg red" , "Source of alcohol" .)