Release old film about backbencher? (6)
I believe the answer is:
exempt
'release' is the definition.
(I've seen this before)
'old film about backbencher?' is the wordplay.
'old' becomes 'ex' (prefix meaning former or onetime).
'film' becomes 'ET' (E.T. the Extra-Terrestrial).
'about' means one lot of letters goes inside another.
'backbencher?' becomes 'MP' (backbencher is a type of Member of Parliament).
'et' going around 'mp' is 'empt'.
'ex'+'empt'='EXEMPT'
(Other definitions for exempt that I've seen before include "Immune - absolve" , "Privileged" , "Freed from liability (to tax etc)" , "Free (from obligation)" , "Release" .)