I don't think gravy on chips is common anywhere in the south. My sister lives in Oxfordshire and sometimes I think she only visits me (in Manchester) so she can get chips and gravy!
The last time I was in a chippy in London I asked for gravy on my chips and the guy behind the counter said "everybody asks for gravy on their chips, we dont do it theres no call for it". What is this pie and mash lark that there into?
I noticed a chippy today on Strutton Ground (off Victoria St, near the Army & Navy) which had a sign in its window, saying it served chips with gravy. If you're interested, it's on the right side of Strutton Ground at the end furthest away from Victoria St.
Apparantly there's a chip shop on the King's Road oppposite the World's End pub that does chips and gravy - or at least, they did "years ago". Incidentally, I was on a rare visit Oop North this weekend and had chips and gravy, having read this thread with interest. Fanbloodytastic - thanks!