The sovereign citizen movement has been around in the UK for ages but it gained a lot of popularity during the Covid lockdowns when certain gullible people started believing anything they read on the internet and thought that they could keep their businesses open by mis-quoting parts of the Magna Carta to the police when they came to shut them down.
Of course it had absolutely no basis in law and they lost all their court cases and got huge amounts of fines, but like
@Time Waster said above, when you're arguing with someone who believes that they are right even when all evidence shows they are not, it doesn't matter to them, they'll carry on believing regardless - they're like the legal equivalent of flat earthers.