I've lived in London all my life and have never come across chips and gravy in a chippie down here.
However, fish and chip shops have almost disappeared in their traditional form around town. Almost all foreign owned now, you're just as likely to to have spring rolls and chow mein on the menu as you are fish and chips.
Chippies still tend to be good on the coastal areas, i had blinding cod and chips in Hastings last year, but generally in the South we have nothing like the the chip shops up North.