Leave European Community, breaking restraint on power (6)
I believe the answer is:
decamp
'leave' is the definition.
(decamping is a kind of leaving)
'european community breaking restraint on power' is the wordplay.
'european community' becomes 'ec'.
'breaking' indicates putting letters inside.
'restraint' becomes 'dam' (I've seen this before).
'on' means one lot of letters go next to another.
'power' becomes 'p'.
'ec' inserted inside 'dam' is 'decam'.
'decam'+'p'='DECAMP'
(Other definitions for decamp that I've seen before include "Abscond" , "Depart suddenly or secretly" , "scarper!" , "Fold up tent and depart" , "Make sudden breakaway" .)