They have weathered the storm of Brexit and Covid, and are fighting the tide of rising inflation. But thousands of Britain’s fish and chip shops could be sunk by the war in Ukraine. At Captain’s, in the seaside resort of Brighton, on England’s south coast, owner Pam Sandhu is normally not one to complain. Yet the shelves of her large refrigerators are empty when they should be full of fresh white fish ready to be dipped in batter and deep fried, then served to hungry customers with piping hot chips. In ordinary times, Russia supplied between 30 and 40 percent of the fish sold in British fish a…