Release old MP covered in film (6)
I believe the answer is:
exempt
'release' is the definition.
(I've seen this before)
'old mp covered in film' is the wordplay.
'old' becomes 'ex' (prefix meaning former or onetime).
'covered in' indicates putting letters inside.
'film' becomes 'ET' (E.T. the Extra-Terrestrial).
'mp' put within 'et' is 'empt'.
'ex'+'empt'='EXEMPT'
(Other definitions for exempt that I've seen before include "Not subject to or liable for" , "Not subject to, taxation perhaps" , "free from tax, say" , "Not subject to a law" , "Free (from obligation)" .)