Metrication in The United Kingdom - 1965 Onwards

1965 Onwards

In 1965, the then Federation of British Industry informed the British Government that its members favoured the adoption of the metric system. The Board of Trade, on behalf of the Government, agreed to support a ten-year metrication programme There would be minimal legislation as the programme was to be voluntary and costs were to be borne where they fell.

Work on adapting specifications started almost as soon as the government first gave its approval in 1965. The BSI took the lead in coordinating the efforts of industry, and where appropriate working with the International Standards Organisation (ISO), CEE, CEN and CENELEC while the Royal Society liaised with professional societies, schools and the like. Initially the BSI targeted 1200 basic standards which were converted to metric units by 1970. Most of the remaining 4000 standards were converted in the ensuing five years.

There were three principal ways in which metrication was implemented:

• Hard metrication which resulted in new products based on rational metric units – for example A4 paper replaced both foolscap and quarto paper and in rugby union 5, 10 and 22 m lines replaced the 5, 10 and 25 yd lines respectively. In many cases the new British Standards were based on existing foreign or international standards, for example ISO 216 (based on the German DIN standard DIN 476) which defined the "A series" of paper.
• Soft metrication where existing standards were rewritten using metric units, but the underlying products remained unchanged: typically standard rail gauge was changed from 4 ft 81⁄₂ in to 1435 mm, a reduction of 0.1 mm, but well within the allowable tolerance of 5 mm. This approach was used where it was impracticable to make any radical changes.
• Revision of measurement techniques were introduced in cases where the concepts behind the existing standard or practice were found to be archaic. One such revision was to define the strength of alcoholic drink as a percentage alcohol by volume rather than, in the case of whiskey, in "degrees proof" (described by Lord Brown as being "based on a test that involves the burning of a given quantity of gunpowder").