If you're using cloudflare you can block counties via that.

I'm also in the UK and run an instance - the problem is that the guidance is too large and overbearing. The stuff that actually mattered hadn't even been released by OFCOM last time I bothered looking, such as the risk assessment.

I guess we'll know more when they release the guidance on age verification - that will be what kills most sites off if they insist its required for all social media

Does it really, practically, impact things?

If people had to obey the law of "every country that has any internet presence", site operators worldwide would have to do such silly things as ban women from using the internet while not sitting right next to their husbands, or who knows what other silly things as per the Sharia. So I don't really see how any such thing is to be taken at anything but grandposturing from boomer political parties, at face value.

Now, if you want to ban Bri'ish IP addresses, your hosting can take care of that. For the most capable ones it's just a flip of a switch. But do consider that in some cases that makes your site worse for everyone else worldwide as such rules are sometimes implemented via privacy-invading systems (eg.: yet another control that makes your site depend on Cloudflare).

This is already impacting futurology.today - one of the Mods is British, and because of this law doesn’t feel comfortable continuing. As they have back-end expertise with hosting, if they go, we may have to shut down the whole site.

Its good news that they are merely a mod and not an admin / op, then! That's why documenting and transfer of knowledge is important! If they don't feel capable of dealing with a stupid law, they should make themselves unnecessary to your community ASAP! Have them prepare to step down from the role by documenting everything that a replacement needs to be able to do, then as soon as another mod can test that the documentation works, derole them if that's what they want.

I have no idea about how people in the UK should react and I'm not a lawyer, but my understanding of it is that if no one involved in running your site is British, it's not hosted in the UK, and you don't have any kind of business relationships with people in the UK, you absolutely should not worry about it or take any action at all beyond making sure you don't sign any deals or offer any products for sale in that country.

They cannot legally or practically do anything to you beyond perhaps blocking access to your site somehow I suppose, and in the extremely unlikely event that they tried something crazy you'd be an international cause celebre with plenty of legal support available. Doing their dirty work for them by trying to block British IP addresses seems inadvisable.