They know they'll find workarounds, they'll just arrest whoever is involved in the workarounds. Law isn't a computer firewall, it's a loaded weapon.

The beauty of VPNs is that you do not need to have a presence in the UK to make or sell one. And there's a huge amount of money in it.

The law is very bad at dealing with such realities, see also piracy and drugs. The last time I checked TPB is still accessible in the UK with only DoH.