I'm a bit like that, too. Most city-centre chippies are SHIT, certainly in comparison with what you're talking about, so I never use them. The majority of the ones in Wrexham are dire. Glasgow and Liverpool do have some good ones, though.
However, for top-notch stuff to rival your favs on the Cornish coast, when I'm 'up the road' I go to an award-winning one in Anstruther (in Fife): http://www.anstrutherfishbar.co.uk/ or there's another one just around the corner, which the locals use, cheaper and just as good :)
Marco.