Most UK vehicle registrations follow a specific format; there are, however, some exceptions. One is for military vehicles, which have followed their own alphanumerical format since 1949. Armed forces plates have either two numbers followed by two letters suffixed by a further two numbers, or for vehicles registered from 1995 onwards, they follow the format of two letters followed by two digits suffixed by two letters. Between 1949 and 1982 the two letters acted as either an indicator for the branch of the services that the vehicle belonged to or the category of the vehicle.

Most armed forces registration plates are black with white or silver characters. The registration mark can be displayed in a variety of ways, across one, two or three rows.

Another exception to the standard registration mark is for trade plates. Motor traders and vehicle testers as assigned trade licences, which allow them to drive unlicensed vehicles on public roads while abiding by certain restrictions. Trade plates can be used, temporarily, on any vehicle and are used to identify the person rather than the vehicle. Since 1970 these plates have consisted of red lettering on a white background. They take the format of three numbers followed by between one and three letters.

Diplomatic plates also follow their own specific format. Vehicles operated by High Commissions, foreign embassies, consular staff and many other international organisations use them. The plates on these vehicles consists of three digits, one letter and a further three digits. The letter is either a D for diplomatic staff or X for accredited non-diplomatic staff. The first three digits act as an identifier of the country or organisation, while the final three digits act as a code, dependent on the role of the operator.