European window destroys Conservative peace (8)
I believe the answer is:
easement
'peace' is the definition.
'european window destroys conservative' is the wordplay.
'european' becomes 'e' (abbreviation e.g. EU).
'window' becomes 'casement' (I've seen this before).
'destroys' indicates named letters should be taken away.
'conservative' becomes 'c' (abbreviation commonly used in UK politics).
'casement' with 'c' taken away is 'asement'.
'e'+'asement'='EASEMENT'
(Other definitions for easement that I've seen before include "right of passage" , "landowner's right" , "The legal right to cross or use another's land" , "Right to cross another's property; peace" , "giving right of access to adjacent area?" .)