I guess I used "loophole" because the whole program is a loophole. Typically exempts you from inspections, no international drivers license needed, you buy coupons that relieve the fuel tax, we use weird number plates as you mention (not the ones from home, but military off-duty plates). I had an old LHD Opel Rekord from Germany when I was in the UK, like this one: https://en.wikipedia.org/wiki/Opel_Rekord#/media/File:Opel_R...