A Market Place advertiser was looking for information on the registration number (plates) of his tractor:-
"I am restoring my 1963 35X. The seat was non existent but I located another tractor dumped on a farm with a 'good' seat.. The number on that tractor is AMW 413B (I have the original rear plate). Obviously the farmer who bought it never re-registered it in Ireland.. I am just curious where it was originally registered. Micheal Hurley"
Tim Reynolds replied with so much information, that it gets a page to itself...
Before 1973, UK vehicles were registered by the local authority (i.e. the County Council, City or County Borough Council). This system started in 1904 and the first registration was A 1. The numbers 1 - 9999 were allocated sequentially, and different letters were allocated to different authorities.
However, the numbers soon ran out and a new system with two letters and 4 digits was introduced (for example AA 1234). This lasted until about 1934 (much later in some places), but the letters were still allocated to authorities, making it possible to trace a vehicle back to it's original entry in a ledger book held by that authority. Registrations with an I or Z were allocated to Ireland and S to Scotland. In 1934, another system started, with 3 letters followed by 3 numbers (e.g. ABC 123). The second two letters were again issued to different authorities, following the previous allocations, with the first letter being a serial. So, for example Oxford CBC (City Borough Council) issued AJO 1 to AJO 999 and then BJO 1 to BJO 999 and so on.
The serial letter allows you to roughly date this series: A-G pre-war - ish, G-Y 1950's.
This lasted well into the 1950's in most parts of the UK, however the more populous places (London) ran out of combinations in about 1957/8 and started a new type with the combination reversed (i.e. 123 ABC). Again the second two letters are the key to the authority. This series lasted until about 1960. There were some authorities that then issued a reversal of the original pre-war series (1234 AB), before a new type of registration appeared in 1963. In this series, the year of registration was indicated by a suffix letter, starting with A for 1963 and B for 1964 etc. Some authorities did not switch over to this type until 1965 however so it's possible to find non-suffixed 1964 vehicles about.
Registrations were centralised and computerised from about 1973 at DVLA, starting initially with new registrations. Older records were transferred in the late 1970's (if the vehicle was taxed), and the old records (usually on a card system plus legers) were either sold, destroyed or put into county records archives, depending on the authority. The allocation of letters to areas continued to follow the old patterns with some changes until the abandonment of the system entirely in 2001.
So to your number. Remember the second two letters are the key, MW being a series allocated to Wiltshire County Council, County Hall, Trowbridge. The preceding A is a serial, but the suffix B indicates the tractor was registered in 1964.
Wiltshire County Records Office ( www.wiltshire.gov.uk/heritage/html/wsro.html ) may hold the pre 1973 index: I can't see any reference though so it may have passed into private hands or been destroyed. The magazine "The Automobile" ran an excellent series about ten years ago on the registration records of the UK and where they can be found, but I can't at present locate the magazine with the Wiltshire details. Unfortunately, it's not possible to access the DVLA records unless you're in the Police Force or similar, however a call to DVLA will usually reveal whether they hold a computer record for the vehicle; it's possible it went to Ireland before the late 1970's and therefore was considered "dead" and the record not set up.