Nothing set up about European ban (4)
I believe the answer is:
veto
'ban' is the definition.
(veto can mean a ban or prohibition on something)
'nothing set up about european' is the wordplay.
'nothing' becomes 'O' (looks like zero - 0).
'set' becomes 'tv' (TV set).
'up' shows that the letters should be reversed in order (in down clue: letters go upwards).
'about' means one lot of letters goes inside another.
'european' becomes 'E' (abbreviation e.g. EU).
'o'+'tv'='otv'
'otv' back-to-front is 'vto'.
'vto' enclosing 'e' is 'VETO'.
(Other definitions for veto that I've seen before include "Right to reject a proposed measure" , "Embargo" , "Refuse permission" , "UN rejection" , "Disallow" .)