Several of the bigger supermaket chains (Tesco, Sainsbury's, Co-op/Somerfield) are running roughshod over the law with impunity, selling milk in non-reusable containers in a mix of 500ml and 568ml sizes along with 1136ml and 1000ml (etc) of course.
Tesco even confuse the issue even more by emblazoning a big "1" on the front of their 568ml milk. Now anyone in an "officially metric" country like ours might assume rightly that the "1" refers to a litre. But it doesn't of course.
You have little chance of comparing prices whilst this is going on, since it seems that only the supermarkets' own-brand milk is treated in this weird way: the rest of the milk on the same shelf is usually in proper metric sizes. As is goat's milk (even own-brand goat's milk)
It's all very confusing for us the customers.
It's even illegal that this is happening but the TSOs appear to take no notice. The milk exemption seems to have been passed to allow the doorstep milk industry time to change to 500ml bottles since of course re-tooling a glass bottle plant takes a bit of time. But as with what happens if you permit dual-labelling, the result was predictable: the doorstep milk people have done *nothing* to change their bottles in the 15 or more years since the exemption was passed.
And so it is with pubs. The tabloids keep wingeing on about how "we must protect the traditional British pint", but actually (apart from the odd quantitiy of 568ml involved) there is nothing traditional about the pints being served in British pubs these days. That's even including the superb "real ales" served by hand-pump or even tapped direct from a keg on the shelf behind the bar. These beers do indeed celebrate the glorous history and traditions of British brewing (thanks, CAMRA), but the quantities they are served in do not.
Modern beers are a *lot* stronger than the beers and ales that our grandfathers would have recognised. Time to drop the quantity a bit to compensate out the strength increase. Even a "half" of some of the current beers are possibly borderline for the drink-drive regulations.
Resizing the "half" to 250ml would help with that (along with resizing the "pint" to 500ml of course). And many bottled or tinned beers come in 500ml containers these days so the same glasses would serve all products equally.