I doubt it heavily. CF has control over a large chunk of the global internet - they're not going to go thru their clients one by one and make sure they're doing age verification. That's absurd and far too expensive.
The alternative to that is either:
1. UK blocks cloudflare (unlikely, come on now)
2. UK gives cloudflare a pass (fairly common)
3. Somewhere in-between. Maybe UK cares about highly visible people behind cloudflare like 4Chan but not others.
Yeah that's option 3, for now. But they won't go after cloudflare in the general case because it's too risky IMO. And cloudflare will only comply to the absolute minimum they can get away with, because they can't burn money auditing every single customer behind cloudflare.
I think if that were true, there would have at least been an attempt at a court case at the very least. But AFAIK every case they have been involved in, they've won. I am not defending their content, merely a right to exist, especially when you're not breaking any applicable laws.
If you want to talk about content that objectively breaks laws... 8chan hosts monkey torture videos.
The alternative to that is either:
1. UK blocks cloudflare (unlikely, come on now)
2. UK gives cloudflare a pass (fairly common)
3. Somewhere in-between. Maybe UK cares about highly visible people behind cloudflare like 4Chan but not others.