Echo - cheap plates from ebay. I've had a few, quick delivery + good quality. Won't cost much more than the Halfords sticker and their delivered to your door.
i had a magnetic L place a few years ago... and it had two magnetic strips at the top and bottom (was a cheap one) and that left a few marks... prob from it slipping slightly when i added and removed it.
I have the GB on my license plate.. not that i have even gone abroad in my car :roll:
Excuse my ignorance, but just to feed my curiosity---what are these GB stickers/magnets/plates for? (the purpose of having them) and why are they required by law? We don't have any such thing over here...
Magnetic are fine and reusable (mine live on the fridge) , just make sure both surfaces are clean. I also use magnetic ones to protect paintwork when using Saris Bones bike rack.