As of 2002 there were reportedly 794,477 recorded registration plates in Northern Ireland, compared to only 50 for the island as a whole when the format was first introduced in 1903.

All possible codes had been allocated by 1957, following which reversed sequences were introduced, the first county to do so being Antrim in January 1958 with 1 IA.

These reversed sequences were completed quickly, leading to the introduction of the current "AXX 1234" format in January 1966, where "XX" is the county code and "A" is a serial letter.

[citation needed] The distinguishing code for the United Kingdom, including Northern Ireland is "UK".

[5] Of the EU countries, a separate identifier is only needed when travelling in Cyprus, Malta, and Spain, as they are not party to the convention.

[notes 1] While motorists with vehicles registered in Great Britain are permitted by the DVLA to use number plates carrying Euro-style bands with UK national flags and country codes (such as ENG, England or SCO), this is not possible in Northern Ireland.

When the UK was a member state of the European Union, it was possible to choose to display number plates conforming to the common EU format introduced by Council Regulation (EC) No 2411/98, with a blue strip on the left side of the plate with the European Union symbol (circle of stars) above the international vehicle registration code of the member state (GB).

[citation needed] After Brexit, other EU countries are no longer required to accept UK "Europlates", as the regulation only requires member states to accept the standard design as a distinguishing sign when displayed on a vehicle registered in another member state.

After this, Euro-plates must be replaced by a number plate that features the UK code (GB before 28 September 2021) in order to be valid as a national identifier.