The UK system associates the plates with your car. This incurs basically two pieces of paperwork online when you sell it, one of which is also annual taxation.
The administration has gradually modernized so that all the legal requirements of tax/registration/insurance can be checked online.
However, there's a loophole that's apparently becoming popular: "ghost plates". Number plates aren't a secure document. They have no authenticity markers. So you can just.. print your own, slap them on, and you're very unlikely to get police attention. A subset of that is plates which are IR scattering so they don't show up on speed cameras.