I think the difference in a standard drink is driven by customary units which tend to be smaller in the UK. A British shot is either 25 or 35ml, while the stand

I think the difference in a standard drink is driven by customary units which tend to be smaller in the UK. A British shot is either 25 or 35ml, while the standard American shot is typically 44ml (1.5oz). British beer is also sold in pint (20 oz) and half pint (10 oz) units, while an American pint will be 16oz across the board. This layout seems to point towards smaller units, with the smallest British unit being 10ml of ethanol (25ml at 40ABV), while the smallest possible American equivalent would be 17.6ml for a 1.5 oz shot. Thus if we’re using a single shot as our measure of a “standard drink”, then Americans will be consuming about 70% more pure ethanol than their British equivalent per drink. Also, health authorities have begun rethinking how much drinking is too much, hence the downward deviation of what the international standards say.