Yes the problem with UK ones though is that they route all the traffic through a prude proxy if you don't register. Because the UK is getting back to the Victorian era.

I had a SIM from three Ireland that tried to apply this UK policy also on the republic of Ireland customers where this is not required. It was unusable, it blocked pretty much everything it didn't recognise like VPNs, even email servers. Luckily there's many sane providers there too. And no they don't require registration.