On February 15, 1971, variously known as Decimal Day, Decimalization Day and D-Day, the United Kingdom and Ireland decimalised their historical currencies. Although both currencies were separate — Irish Pounds and British Pounds — they were at the time tied to each other at fixed 1–1 exchange rate.

Under the old currency of pounds, shillings, and pence, the pound was made up of 240d (pence). Under the new it was divided into 100 pence. For details of the currency before decimalisation, see Pre-decimal British coinage and Irish pre-decimal system. Interestingly, the face value of Maundy money was instead maintained, effectively increasing all coins' value by a factor 2.4, as the coins continue to be legal tender.

The changeover was expected to take several months to take effect but shopkeepers found that they couldn't accommodate the old and new coins in cash registers so they quickly bagged the old coins, lodged them in the bank and they were never re-issued so the new system was effective within a couple of weeks. A public information campaign which had run over the preceding two years and the willingness of a young population to embrace the change also helped. In general, elderly people had more difficulty adapting and the phrase 'How much is that in old money?' became a metaphor for someone who couldn't make the change to other new systems, for example the metric system of weights which was adopted many years later.

In the UK, consideration was given to having a new "decimal pound" worth ten shillings in the old currency which would have resulted in the "decimal penny" being worth only slightly more than the old penny; in the event, it was decided that Pound Sterling's importance as a reserve currency meant that the Pound should remain unchanged.

One old British penny

One new British penny

One new Irish penny

See also

• Decimalization

• British coinage
• British banknotes
• UK topics