From what I understand OfCom has been heavily defunded under the tories so how much they will be able to police the net when they already can't do the tasks they already had.
If you are from the UK and want to really hit the Tories where it hurts I'd suggest filing OfCom complaints about untruths on the newswebsites of the rightwing media (Think the Sun, The Telegraph, The Financial Times etc.) They where especially happy to publish clear untruths about the EU. (Something about bendy bananas vaguely comes to mind.) Hey It's illegal now

Also helps if you can catch large Tory donors and politicians lying on the internet and report that.
There is no better way to hit a political party than to limit the way they raise funds and gather votes.
Well yes and no. There might be treaties and such that may allow for one country to extradite a citizen of another country to face trail in the first country for crimes committed there. It is a lengthy process that can result in a hard no for various reasons.
But if that fails economic, military and soft power come into play. All of which the UK is lacking on since Brexit. Soft power has been squandered by the dozen Tory leaders over the last decade (trying to crash the world into an economic crises is not appreciated by other leaders). Economic, the UK needs the other countries more then they need the UK as their reliance on imports has heavily increased and they don't have the backing of the EU anymore to give their words weight and militarily they can't do shit because the US and EU will get really mad and show the UK how much the UK needs them economically.
If the EU is good at one thing it is writing laws. (I don't always agree with them but on a whole they are a net positive). It is not easy wrangling over two dozen countries with a napoleon complex, very different cultures, wants, needs and levels of economic development and get them to agree on anything.