Metrication in the United Kingdom

Metrication in the United Kingdom is the process of introducing the metric system of measurement in place of imperial units in the United Kingdom.

Metrication in the United Kingdom remains equivocal and varies by context. Most of government, industry and commerce use metric units, but imperial units are officially used to specify journey distances, vehicle speeds and the sizes of returnable milk containers, beer and cider glasses (though fresh milk is often still sold in multiples of pints, with the metric equivalent also marked). Imperial units are also often used informally to describe body measurements and vehicle fuel economy. In schools, the use of metric units is the norm; however, schools must also teach children about those imperial units that remain in common usage in the UK.

Adopting the metric system was discussed in Parliament as early as 1818 and some industries and even some government agencies had metricated, or were in the process of metricating by the mid 1960s. However, a formal government policy to support metrication was not agreed until 1965. This policy, initiated in response to requests from industry, was to support voluntary metrication, with costs picked up where they fell. In 1969 the government created the Metrication Board as a quango to promote and coordinate metrication. In 1978, after some carpet retailers reverted to pricing by the square yard rather than the square metre, government policy shifted, and they started issuing orders making metrication mandatory in certain sectors. In 1980 government policy shifted again to prefer voluntary metrication, and the Metrication Board was abolished. By the time the Metrication Board was wound up, all the economic sectors that fell within its remit except road signage and parts of the retail trade sector had metricated.

The treaty of accession to the European Economic Community (EEC), which the United Kingdom joined in 1973, obliged the United Kingdom to incorporate into domestic law all EEC directives, including the use of a prescribed SI-based set of units for many purposes within five years. By 1980 most pre-packaged goods were sold using the prescribed units. Mandatory use of prescribed units for retail sales took effect in 1995 for packaged goods and in 2000 for goods sold loose by weight. The use of "supplementary indications" or alternative units (generally the traditional imperial units formerly used) was originally to have been permitted for only a limited period. However, that period had to be extended a number of times due to public resistance, until in 2009 the requirement to ultimately cease use of traditional units alongside metric units was finally removed.

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