Old relation in favour of European support (8)
I believe the answer is:
forebear
'old relation' is the definition.
(a forebear is an ancestor)
'in favour of european support' is the wordplay.
'in favour of' becomes 'for' (being for a particular cause).
'european' becomes 'e' (abbreviation e.g. EU).
'support' becomes 'bear' (bear can mean to support or carry).
'for'+'e'+'bear'='FOREBEAR'
(Other definitions for forebear that I've seen before include "one from the past" , "Person from whom you are descended" , "One of an earlier generation" , "Older relative" , "Ancestor" .)