I'm unfortunately returning a sausage (6)
I believe the answer is:
salami
'a sausage' is the definition.
(I know that salami is a type of banger)
'i'm unfortunately returning' is the wordplay.
'unfortunately' becomes 'alas' ('alas' is used to express regret).
'returning' says the letters should be written backwards.
'im'+'alas'='imalas'
'imalas' reversed gives 'SALAMI'.
(Other definitions for salami that I've seen before include "One kind of tactics" , "Highly seasoned fatty sausage" , "Highly seasoned Italian sausage" , "Highly spiced sausage" , "Cured meat" .)