But doesn't having the original plates in your boot then appear to be an admission of guilt?
The whole "I am sorry officer, I did not realise they were not road legal" kinda looks a bit moot when you follow it up with "but I have the originals in the car, I will change back now".
I bought my pressed plates from a company called Cottage Promotions/Europlates in Middleport, Stoke on Trent. Went in with my documents and driving licence and picked them up the next day. They are UK legal, reflective in the correct font, and more importantly they have the suppliers postcode and the correct BS (British Standards) mark on them. You also get a handy little card giving you the details to hand to any officer/vosa officer if they question the number plates legality.
67buggers: I know of plenty of people who have been stopped and warned because of their plates. My friend Amy has been stopped and warned with similar UK Legal pressed plates on.