TV inspector impolite about good Dickensian halfwit (7,5)
I believe the answer is:
barnaby rudge
'dickensian halfwit' is the definition.
(character in Dickens' Barnaby Rudge)
'tv inspector impolite about good' is the wordplay.
'tv inspector' becomes 'Barnaby' (Tom Barnaby from Midsomer Murders).
'impolite' becomes 'rude' (similar in meaning).
'about' means one lot of letters goes inside another.
'good' becomes 'g' (abbreviation).
'rude' enclosing 'g' is 'rudge'.
'barnaby'+'rudge'='BARNABY RUDGE'
(Other definitions for barnaby rudge that I've seen before include "Early Dickens novel" , "story" , "Ruby bandager (anag) - Dickens novel" , "Eponymous Dickens novel" .)