Are you guys sure supermarkets are more expensive in the south? I would have thought they would charge the same. When people post up deals on HotUk deals they are the same price for everyone...
I know Tescos price regionally as the one in Amersham we use is supposed to be one of the most expensive in the country according to the local news. I guess it all comes own to things like land costs. It will obviously cost more to rent a very large shop near London than pretty much anywhere else in the UK so the prices reflect this.