Green’s Dictionary of Slang

(UK Und.) to change the number plates of a stolen car.

2004

(con. 1990s) N. ‘Razor’ Smith A Few Kind Words and a Loaded Gun 369: They would not only steal the car [...] they would also ‘plate’ it as well. ‘Plating’ is changing the number-plates of a stolen car to the plates of a legit car of the same make, model and colour.