We can trace the UK car registration system back to 1903. The Motor Car act came into force On January 1st, 1904 and required all vehicles in the United Kingdom to carry registration number plates. County and Borough Councils originally issued the registrations and number plates. This lasted until 1974 at which time the Department of Transport took over by using specially equipped Vehicle Registration Offices (VROs).
The individual councils were issued with one or more letter codes for registering vehicles, and both one and two letter codes were issued from 1903. This original system used a one or two letter area code and between one and four numbers. For example: A1 up to AA9999, but by the 1930's these had run out and so a new system was needed.
A1 - YY9999 : 1903 - 1930's
AAA1 - YYY999 : 1930's - 1960's
During the 1930's the single and double area code registrations became obsolete and 3-letter area codes became necessary. This was in the form of an extra serial letter added to the front of the original letter codes. These new registrations where first used around 1932, but due to the standard size of number plates it could only accomodate 3 numbers and these where rotated in conjunction with the first registration letter. For example ADA999 would rotate over to BDA 1.
AAA - 999YYY : 1950's - 1960's
In the 1950's the system was reversed by councils who had run out of combinations in the previous series, now with the numbers prefixing the letters (e.g. 237RYU). A small number of councils ran out of these numbers by the late 1950's / early 1960's and as a temporary measure, four number / one or two letter area code registrations were issued (e.g. 2345AA). These did not have a serial letter, the one or two letters being the area codes as originally issued in the reversed format. Only the single letter area codes D,E,F,H,K,N,R,U and W were issued in this reversed format (e.g. 1042D) between 1953 and 1962. This was the last time the single letter area codes were used. Not all of these numbers were issued, making this type of number rarer than the ABC123 type. Some of these numbers are now being auctioned off as personalised registrations.
AAA1A - Y999YYY : 1963 - 2001
By the 1960's, some of the busier councils began to run out of numbers again and it was clear an extra letter or number was needed on the plates. From 1963 the suffix letter "A" was added to the registrations of some busier councils (e.g. NAT233A), the letter changed to "B" in 1964 and so on. Not all councils used the "year suffix letter" until 1965 when the "C" suffix was issued and the addition of the year letter became compulsory. On 1 October 1974, registrations were centralised, and some area codes changed.
In 1983, the year letter suffix system ran out and it
was replaced with a year letter prefix system. This system operated in
the same format, but reversed (e.g. A234UUV). There is more information
about these year suffix and prefix codes on the age identifier pages.
The suffix and prefix letters I,O,Q,U and Z have not been used. The year
prefix system ran out with the "Y" prefix on 31 August 2001.
AA51AAA : September 2001 onwards
The current system of number plates is based around the old practice of year and area identifiers but a new, simpler system of codes has been introduced.
In the above example, the AA is the area code and 51 the age identifier. The age identifier changes every 6 months in March and September as before, but gives an 'at a glance' idea of the age of the vehicle with 51 representing September 2001 to February 2002, 02 March to August 2002, 52 September 2002 to February 2003 and so on. The final three letters are serial letters, and for the first time in the UK the letter Z is permitted (only in the serial letters and not in the area code).
The new area codes are listed here and apply to new vehicles registered from 1 September 2001 onwards - vehicles that date before this time will continue to use the previous system. The new system has been designed to last for at least 50 years and if reversed (i.e. AAA 51AA) could last until 2099.