.co.uk is run by the same people as .uk. There is no additional org that you trust when you register a .co.uk: https://en.wikipedia.org/wiki/.uk#Second-level_domains
> do browsers have a wildcard suffix list
Yes: https://publicsuffix.org/ and they have discussed this situation here: https://github.com/publicsuffix/list/issues/2306
Yes, Japan does the same with .co.jp but also .ne.jp, ac.jp, etc.
I know about the public suffix list - I was wondering about the wildcard specifically. In the very issue you linked to, as of 2025, it seems this was still unresolved...:
> We have no plans to modify the .name entries at this point in time. We are aware of the implications of adding a wildcard, therefore we won't.