Never encountered that in London or East Anglia. What I do find is that the definition of "large", as in "large cod", has become somewhat flexible. In the main chippy in Newmarket, it's a piece that extends over the edge of the plate. In the one in a nearby village, part of a chain of chip shops, it is now what would be called 'medium', at best, since it got taken over by the chain. "Small" is not a term they use, preferring to settle for just 'cod', but it appears to be a piece which has to be searched for under the chips. "Large" in "large chips", however, is not affected by this shrinkage.