was introduced in 1917 by the UK government. The letter D was assigned to Dublin. Upon the establishment of the Irish Free State and later, the Republic of Ireland, the Irish government retained the designation and today it forms part of the Eircode system. Since Irish independence, D has never been reassigned as a postcode area in the UK. Modern postcodes throughout the Republic of Ireland take a slightly different form from UK postcodes and are specific to individual addresses. Non-geographic postcodes A number of non-geographic postcode sectors are also contained within geographic postcode areas. GIR GIR 0AA is a postcode created for Girobank in Bootle. It remained in use by its successors when Girobank was taken over by Alliance & Leicester and subsequently by Santander UK. BF The BF postcode area was introduced in 2012 to provide optional postcodes for British Forces Post Office addresses, for consistency with the layout of other UK addresses. It uses the national non-geographic post town "BFPO" and, as of 2012, the postcode district "BF1". BX The non-geographic postcode area BX has been introduced for addresses which do not include a locality: this allows large organisations long-term flexibility as to where they receive their mail. This postcode area is used by Lloyds Banking Group (BX1 1LT), HSBC (BX8 0HB) and parts of the HM Revenue and Customs like VAT Central Unit (BX5 5AT) and Pay as You Earn (BX9 1AS). Lloyds Bank also use BX4. After splitting from Lloyds, TSB Bank uses BX4 7SB, the latter part of which, when written, looks similar to "TSB". XX The non-geographic postcode area XX is used by online retailers for returns by Royal Mail, and for COVID-19 test samples. Overseas territories Certain British Overseas Territories introduced single postal codes for their territory or major sub-sections of it. These are not UK postcodes, even though many are formatted in a similar fashion: Other overseas territories have introduced their own more extensive postcode systems: Civilian residential and business addresses in Akrotiri and Dhekelia are served by Cyprus Postal Services and use Cypriot postal codes. Mail to Overseas Territories is treated as international if posted in the UK. See also List of postcode areas in the United Kingdom by population List of postcode districts in the United Kingdom Postcodes in the United Kingdom UK Postcode Regions by Population List of Eircode routing areas in Ireland Notes References External links Office