I think just getting blocked is no big deal, but they'll probably get fined as well, that is the problem

What mechanism does the UK government have to extract fines from Wikipedia?

“Pay this or we will concoct some criminal charges on your entire leadership team, append each of you to interpol lists and formally request your extradition” is probably a good start.

Good luck with that. The US has that power, the UK doesn't.

The UK might not have the power to force extradition (neither does US, in fact), but to make life very inconvenient for someone - for sure.

Probably, my understanding is theyve already implemented IP blocking to other sites.