Pubs will soon be able to offer a two thirds of a pint measure under new government plans.
The proposal for a new imperial glass size comes after pressure from the pub trade to allow more flexibility in serving draught beer and cider - particularly higher strength versions.
However the government has moved to reassure people the measure will not replace the traditional pint.
The plans, to become law "at the first available opportunity", were unveiled in a government response to the National Measurement Office's consultation on specified quantities. It also includes proposals to:
• Deregulate wine servings of less than 75ml, allowing for more flexibility at wine sampling and tasting sessions
• Replace the existing specified quantities for fortified wines with smaller sizes of 50ml and 70ml, bringing the law into line with current trade practice
• Bring the sale of brandy into line with other spirits by requiring its sale in specified quantities of 25ml and 35ml
Lord Drayson, science and innovation minister, said: "There is no question of replacing the British pint, but introducing the option of a new imperial measure is good news for consumers, providing them with more choice."
The British Beer & Pub Association welcomed the announcement.
Chief executive Brigid Simmonds said: "We are delighted the government has legalised the two thirds of a pint, for which the BBPA has been lobbying long and hard for many years.
"Pubs will now enjoy greater flexibility and our customers will now be able to have even greater choice about how to enjoy their beer."
But Tony Payne, chief executive of the Federation of Licensed Victuallers Associations, said a new measure could be confusing for drinkers.
"If some pubs have it and some pubs don't that could be confusing for customers. I just can't see many pubs doing this."
He also suggested that people who normally drink a half could be encouraged to go for a two thirds.
Meanwhile the Wine and Spirit Trade Assoctiaiton welcomed the wine sampling proposal. Jeremy Beadles said:
"Deregulating wine measures below 75ml is a welcome move that the WSTA and our members have long been arguing for.
Chief executive Jeremy Beadles said: "This flexibility will give consumers the chance to sample small measures of the huge variety of wines out there, letting them broaden their knowledge and taste everything from the finest and rarest to the most innovative and experimental."