On the other hand, the limited size of the British market limits Parliament’s ability to pressure foreign companies.

China may be able to bully Apple into letting it snoop on its citizens’ icloud backups, but when the UK wants the same illiberal snooping powers, with 10% the population it’s 90% easier to walk away.

It's quite ironic that they would have an easier time enforcing that if they were still part of the EU and could have been the deciding factor towards more regulation faster.

The EU is big and rich enough to force Big Tech into submission under threat of loosing the market.

Significantly less than 10%.