Southern firm exploit northern dish (6)
I believe the answer is:
scouse
'northern dish' is the definition.
(also lobscouse, a northern English stew)
'southern firm exploit' is the wordplay.
'southern' becomes 's' (abbreviation).
'firm' becomes 'co' (a firm is a company).
'exploit' becomes 'use' (use is a kind of exploit**).
's'+'co'+'use'='SCOUSE'
(Other definitions for scouse that I've seen before include "another city's dialect" , "Liverpool accent" , "Liverpudlian (stew)" , "Liverpudlian accent" , "Liverpudlian (colloq.)" .)