Sudden flight impressed European (8)
I believe the answer is:
stampede
'sudden flight' is the definition.
'impressed european' is the wordplay.
'impressed' becomes 'stamped' (stamping is a kind of impressing).
'european' becomes 'E' (abbreviation e.g. EU).
'stamped'+'e'='STAMPEDE'
(Other definitions for stampede that I've seen before include "herd scatter wildly" , "rush for safety maybe" , "Panic-driven rush of herd of animals" , "Rampage" , "Deems apt to have flight of cattle" .)