4chan is showing ads on their site, but if your idea had any grounds, the issue would be with the ad network, not 4chan.

It's hard to understand the logic of this statement. Why the ad network? 4chan business is to show ads to users while offering them a platform for conversations. What 3rd party service do they use is irrelevant unless that is by coincidence an UK company.

More realistically, 4chan will likely be banned by UK ISPs after a court ruling.

This is exactly what my comment above means.