<P> The changeover to selling of petrol by the litre rather than by the gallon took place after the Board was wound up . It was prompted by a technical shortcoming of petrol pump design: pumps (which were electro - mechanical) had been designed to be switchable between metric and imperial units, but had no provisions for prices above £ 1.999 per unit of fuel . Once the price of petrol rose above £ 1 per gallon, the industry requested that they be permitted to sell fuel by the litre rather than the gallon, enabling them to reduce the unit price by a factor of about 4.5 and so to extend the lives of existing pumps . </P> <P> In the United Kingdom, draught beer and cider are the only goods that may not be sold in metric units; the only legal measures for these are ⁄ pint (190 ml) (rarely encountered), ⁄ pint (283 ml) and multiples of the pint . Other alcoholic drinks for consumption on the premises are sold by metric measure: the ⁄, ⁄ and ⁄ gill measures for spirits (whisky, gin, rum and vodka) were replaced by 25 ml and 35 ml measures on 1 January 1995 and since 1995 wine may only be sold in 125 ml, 175 ml or 250 ml glasses . (Prior to 1995, the size of wine glasses was unregulated .) </P> <P> Before the Hodgson Committee, the metrication process was already in operation . One example was the Ordnance Survey, the national mapping agency for Great Britain, which initiated the Retriangulation of Great Britain in 1936, using metric measures . A metric National Grid was then used as the basis for maps published by the Ordnance Survey from World War II onwards, the War Office maps having had a metric grid since 1920 . The Ordnance Survey decided on full metrication in 1964 . The best - selling 1 inch to the mile range of maps started being replaced with the 1: 50000 range in 1969 . The metrication of Admiralty Charts began in 1967 as part of a modernisation programme . As of 2013, road and street maps with primary scales in inches per mile were still being produced by the company Geographers' A--Z Street Atlas. (1) (2) </P> <P> Another example was the Met Office who, in 1962, started publishing temperatures in both Celsius and Fahrenheit, dropping the use of Fahrenheit from their official reports in 1970 . </P>

When did britain change to the metric system