Adamm what size is your plate?
6 Character Reg UK Car Oblong 16 1/8" x 4 3/8" - 410mm x 111 ???
http://www.craigsplates.com/standard-yellow-or-white-acrylic
i've got the same as these.
As long as u stick to the UK size lettering, dont do stupid fonts, spacing etc then you will be fine.
just ordered some german pressed plates for mine.
hope i dont get stopped by the plod much