I personally would boycott any shop or supermarket that sold food that was raised on lower standards than presently applied in the UK and Europe, especially so with chlorinated chicken sheds where chickens are raised very very poorly. The chlorine washing isn't the issue itself but the chickens are cleansed that way after death to make up for very poor standards of life and wellbeing of the birds while alive, what with cramped conditions, illness and poor sanitation. I seriously doubt many/any current supermarkets in the UK will want to sell chlorinated chicken anyway and haven't some already stated that they won't?
That said I'm 90% vegetarian nowadays and only eat fish from time to time (I guess I'm pescatarian ) so I wouldn't be eating any chicken one way or the other