Statutory Instrument 427 of 1999
These regulations carry out the Vehicle Registration and Licensing Act: how to apply to register a vehicle, the number plates and the third plate, temporary identification, vehicle licences and garage licences, with the forms for each.
Section 11 is the third plate. This copy says it goes on the windscreen; since SI 43 of 2016 it may also go on a quarter glass or a side window.
The fees printed in the Third Schedule here are the ones from 2013. They were replaced in January 2026 by SI 10 of 2026, so use that table, and confirm at the registry before you pay.
The VID papers, the licence codes and the rules these laws set, as questions with the reason behind each answer.