Millennium registrations are slightly more complex than other types of registration, but contain more information about the registration.
The first part of a millennium registration contains the issuing town - each two letter combination relates to an area in the UK - for instance the combination NX covers vehicles registered in the North and under the governance of Stockton DVLA office. SA is a Scottish registration from the Glasgow office, and LO is a London registration under the Stanmore office.
Following the two-letter combination comes a two-digit year identifier. The essential difference between prefix and suffix year identifiers, and millennium year identifiers, is that the year identifier on a millennium plate is a number, not a single letter, and that there are two millennium releases each year.
This is expressed in the millennium system as a two-digit number combination, starting at 51 (a 5 denotes a September release). So 51 millennium registrations were released in September 2001. The next number in the range is 02 (the first part of 2002), followed by 52 (September 2002), 03, 53, 04, 54, and so on.
Following the town and year identifiers come three more letters, which have no significant meaning.