Although I'm now in Yawkshire, and starting to pick up the accent a tiny bit, I still have a horrible Estuary accent and say things like "Taaahn" for town and "Miwlk" for milk. I can't even attempt to say "towel rail" so I hang them on the door corners instead.
Many many years ago, when a friend and I did a summer night-ride to Broadstairs from Dartford, I heard a real Kentish accent from a young girl in the cafe-bar on the seafront. I wonder if the original Kent accent survives at all now, due to the number of Londoners who moved out there.
I've noticed the strongest, "roughest" if you will, accents occur in major port towns and cities. Cockney, Scouse, Geordie, I reckon it must have been a real mix of people that started those accents.