They're not blocking them, they're actively seeking fines, even after the site takes it upon themselves to block the UK.

Ah, now that's silly of our dear UK Govt. Bit of an overreach there, and oh definitely they'll get bitch slapped.

It would be a lot easier for the UK to just block any site they don't like. Especially when the concern is ostensibly to protect UK citizens from harm.

They already block the pirate bay website. Could have done the same thing with these sites but ...

But Ofcom is in fact saying that you are _not_ free to run those websites from the UK and they expect _you_ to implement a perfect blockade of UK IP addresses. On the other hand, if Ofcom receive a tip-off from a random charity claiming they found a UK IP address which doesn't get blocked for 10 minutes or whatever the hell happened here then they will try to extrajudicially internationally fine you for it.