It doesn't matter where you park lads, my dad's number plates were stolen off his TT on the driveway!
I don't want to make you worried or anything, but the number plates usually hide the ID of a stolen car they then use to steal fuel and break in to people's houses. The Police should investigate every time the plates are caught speeding etc. and not send you the fine unless it's obvious it's not you. But it's likely they'll try you first! Lol!
They caught the guy who stole my dad's plates, he wasn't very clever about it though, he put the plates on a different colour car and it was the mk1 tt, not the mk2 like my dad's. So it was easy to spot the fake!