European Union rules drafted in 1999 aimed to phase out imperial measures such as miles and pints by 2009, but the EU's executive body decided on a U-turn Tuesday in the face of public opposition.
The decision "honors the culture and traditions of Great Britain and Ireland, which are important to the European Commission," said Guenter Verheugen, the EU's industry policy commissioner.
Britain and Ireland, like almost all countries around the world, officially use the metric system, but imperial measures are often still used alongside metric counterparts.
Under the EU decision, they can maintain miles on road signs and pubs may continue to serve draft beer in pint mugs. Pint-sized milk bottles will also be retained, along with the Troy ounce for weighing precious metals.
Other goods must already be sold in metric quantities, although traders can also display imperial equivalents.
British politicians welcomed the reprieve for the mile and pint when it was first announced by the commission in May, although pro-metric campaigners warned that sticking to the old system risked hurting Britain's role as a world trading power.
Verheugen rejected such concerns, saying the imperial measures could help trade relations with the United States, which has its own set of measures similar to those used in Britain.
According to the U.S. Metric Association, only the United States, Liberia and Myanmar have not officially adopted the metric system.
The British campaign against the metric system made headlines in 2001 when a grocer was convicted for refusing to sell bananas by the kilogram. Steve Thoburn, who became known as the Metric Martyr, was found guilty of breaching the Weights and Measures Act and given a conditional six-month discharge. He died in 2004.