[michaelt]

China and Russia kicked out Google/Gmail - which was only possible thanks to a firewall - and by so doing allowed local competitors to thrive. Obviously it also gave them a bunch of political control, so we can only speculate about the relative importance of protectionism vs control when deciding to create the firewalls.

Once the UK has a firewall, they could also decide to block Google out of protectionism. Or (perhaps more likely) they could block smaller foreign companies with less political clout and more UK competition.

Of course, I hope they don't; it'd seem like a pretty bad decision to me. But the current conservative government doesn't have many tech-literate members - witness this very proposal! - so a bad decision is entirely possible.