We haven't been to the UK since 2010 but we're stopping in London for a few days this October so we're going to be seeking out a good Fish and Chip place too.
Our previous visits to Fish and Chip places in the UK after researching "best of places" have been a bit mixed. I didn't like how some of the small chippy shops seem to pre-fry their fish and have it sitting there under a heat lamp. I also find the batter to be typically a bit heavy compared to what I like nowadays, which is a more lighter, tempura-like batter. At the places that were made to order however, the fish inside was pretty moist and delicious.
I'm probably going to google a list of "best of's" and "top 10's" again and pare the list down to according to what places show up across lists, seem to be made to order, and ideally have a lighter batter.