Disturbed couple imprisoning Northern composer (7)
I believe the answer is:
'composer' is the definition.
(I know that Poulenc is a composer)
'disturbed couple imprisoning northern' is the wordplay.
'disturbed' indicates anagramming the letters (the order of letters is disturbed).
'imprisoning' indicates putting letters inside.
'northern' becomes 'n' (abbreviation e.g. N. Ireland).
'couple' is an anagram of 'poulec'.
'poulec' going around 'n' is 'POULENC'.
(Other definitions for poulenc that I've seen before include "He's composed" , "Francis ------- (1899-1963), French composer" , "Francis -, twentieth century French composer" , "French composer, d. 1963 - clone up (anag)" .)