It's something russia has been doing for a decade and got pretty good at.

A long term blanket vpn ban is not compatible with a modern digital infrastructure, but with certain protocols (openvpn, wireguard) they can detect their usage and filter them out when necessary.

It does require a lot of expensive DPI (deep packet inspection) hardware I'm not sure UK has, so building a Great Firewall of Britain (Hadrian's Firewall?) will take some time.