UK postal codes are known as postcodes.
UK postcodes use letters and numbers. The British Prime Minister's postcode at 10 Downing Street is SW1A 2AA.
These codes were started by the Royal Mail over a 15-year period from 1959 to 1974 – the full list is now available electronically from the Royal Mail as the Postcode Address File. They were made to help electronically sort mail.
Postcodes are now used for many other purposes such as insurance calculations, and as a way to describe United Kingdom places to sat navs.
See also List of postcode areas in the United Kingdom.