Beer and cider are the only drinks that are legally not sold by metric volume in the UK. They have to be served by the pint, 2/3, 1/2 or 1/3. Every other drink has to use metric.
But that just means the quantity has to be expressed in metric units, possibly in addition to imperial, correct? E.g. I currently have a carton of milk in my fridge that’s labelled “2272ml 4 pints”.
Not for alcohol measures. Beer and cider have to be sold in pints, and there is a list of allowed sizes used for other drinks. Also the size of the standard measure used for spirits needs to be displayed on a sign at the bar.