Conservative perhaps lying about the European disaster (7)
I believe the answer is:
debacle
'disaster' is the definition.
(synonyms)
'conservative perhaps lying about the european' is the wordplay.
'conservative' becomes 'C' (UK political abbreviation).
'perhaps lying' becomes 'abed' (lying abed).
'about' says the letters should be written backwards.
'the european' becomes 'le'.
'c'+'abed'='cabed'
'cabed' back-to-front is 'debac'.
'debac'+'le'='DEBACLE'
(Other definitions for debacle that I've seen before include "Rout; fiasco" , "great failure" , "Total collapse or defeat" , "Pasting" , "Rout; disaster" .)