Boast about European Union, right, for one could wreck things (8)
I believe the answer is:
saboteur
'one could wreck things' is the definition.
'boast about european union right' is the wordplay.
'about' indicates an anagram.
'european union' becomes 'eu'.
'right' becomes 'r' (common abbreviation).
'boast' with letters rearranged gives 'sabot'.
'sabot'+'eu'+'r'='SABOTEUR'
'for' is the link.
(Other definitions for saboteur that I've seen before include "He destroys in order to subvert" , "One who deliberately subverts" , "Political wrecker" , "Rue boast about one who inflicts deliberate damage" , "One deliberately damaging equipment etc" .)