In the south Hoddesdon (lived there for 4 years) and particularly the Rye House area. Also nearby Harlow has no redeeming features. Also Clacton in Essex could do with being swamped by the sea.
Midlands – Wolverhampton – had to walk through it in a suit once and was conscious I was being closely watched by the locals. Really didn't like Leicester on the occasions I have been there.
North – Bradford (used to go to school there), Blackpool (where chavs from every sh*thole go and see if they can out do each other in wearing fake gold jewellry, shell suits and trainers), and Sunderland (even the pound shops have shutters).
Wales – Port Talbot surely takes some beating.
Scotland – Shotts – possibly the most dismal place I have ever had the misfortune to visit.
South West – Bridgwater, Weston-super-Mud and Plymouth are all depressing places IMO.