Well, Northampton is a strange place. The folk who come from the old parts of Northampton have an accent that is across between a watered down Somerset and Norfolk, very ooh aah me duck.
A large portion were evacuated from London to Northampton during WW2 and more came during the mid 70's recession with the promise of cheap housing, so that adds a bit of mockney to the accent.
Milton Keynes to the south is a lot more "home counties" with both posher and cockney-er accents.
A Northern accent definitely starts after Watford Gap (not in Watford) going into Leicestershire.
We definitely don't have a brum accent and get multiple ITV regions.
Odd!