This is a little bit different, this seems to be specifically something to do with Johnson's fixation on Churchill who drank Pol Roger by the (many) pint(s). You'll notice it's not about the plebs drinking cooking wine by the pint. But politically it just seems an open goal to his opponents, when in the real world most champagne producers (except perhaps Pol Roger as some kind of premium Churchill thing) are not going to make a custom bottle for the UK market, the costs of custom bottles mean that 568ml will probably sell for the same as 750ml.