European belts up A1 (6)
I believe the answer is:
superb
'a1' is the definition.
(A1 is old-fashioned slang for superb)
'european belts up' is the wordplay.
'european' becomes 'serb' (person from Serbia).
'belts' is an insertion indicator (inserted letters are tied or belted up).
'serb' going around 'up' is 'SUPERB'.
(Other definitions for superb that I've seen before include "First-class" , "Really excellent, brilliant" , "Excellent, magnificent" , "Dazzling" , "First class" .)