By the glass
Type
Measures
Still wine
125ml, 175ml, multiples of 125ml and 175ml
Port, sherry or other fortified wine
50ml, 70ml, multiples of 50ml or 70ml
Gin, rum, vodka and whisky
Either 25ml and multiples of 25ml, or 35ml and multiples of 35ml (not both on the same premises)
Draught beer and cider
Third, half, two-thirds of a pint and multiples of half a pint
There are no specified quantities for sparkling wine or yellow wine by the glass or spirits other than gin, rum, vodka and whisky.
Here you are Minty......are you opening a pub? (^_*)
https://www.gov.uk/weights-measures-and-packaging-the-law/specified-quantities