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.

Though it was first discussed in the Parliament as early as 1818, a formal policy of metrication only started in 1965. This policy, initiated in response to requests by industry, was voluntary on a sector-by-sector basis, with costs picked up where they fell. In 1969 the Metrication Board was set up to coordinate the programme. Only in 1978, after a carpeting chain store reneged on a voluntary metrication agreement, did the government start issuing orders making metrication mandatory in certain sectors. When the Metrication Board was wound up in 1980, all the economic sectors that fell within its remit apart from road signage and parts of the retail trade sector had been metricated.

Under its treaty of accession to the European Economic Community (EEC) in 1973, the United Kingdom was obliged within five years to incorporate into domestic law all EEC directives, including the use of a prescribed SI-based set of units for many purposes. By 1980 most pre-packaged goods were sold using the prescribed units, the conversion having been either theoretically voluntary or made under United Kingdom-initiated legislation. The mandatory use of prescribed units for retail sales only took effect in 1995 for packaged goods and in 2000 for goods sold loose (for example potatoes or bananas) or from bulk (for example, cheese or meat which is cut and weighed it in front of the customer). The use of "supplementary indications" (non-prescribed units given alongside the prescribed units) was originally to be permitted for a limited period only, but that period was extended a number of times and in 2009 the "sunset clauses" relating to the use of supplementary indicators were removed.

British scientists, philosophers and engineers have been at the forefront of the development of metrication – in 1668 John Wilkins first proposed a coherent system of units of measure, in 1861 a committee of the British Association for Advancement of Science (BAAS), including William Thomson (later Lord Kelvin), James Clerk Maxwell and Joule among its members, defined various electrical units in terms of metric rather than imperial units, and in the 1870s Johnson, Matthey & Co manufactured the international prototype metre and kilogram. However the British Government has been lukewarm in its support of the metric system and, in the words of the Daily Telegraph, the British public lacks cultural empathy with the system.

As of 2012, metrication in the United Kingdom remains partial – 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 and are often used informally to describe body measurements and vehicle fuel economy. At school, the use of metric units is the norm, though pupils are taught rough metric equivalents of those imperial units still in daily use.