I would strongly disagree with that, in the sense of the layer of communication that 4chan operate at. I would argue that 4chan aren't sending packets to the UK any more than I'm currently sending my keystrokes to wherever you are reading this from - these actions are performed at a different layer.

If the UK wants to block packets from across the pond, they should (but I hope they don't) do it via a Great Firewall, rather than expecting random foreign websites to do it for them.