Nobody owns the .co part of .co.uk. If you buy foo.co.uk, that is registered with Nominet, who are the registry for .uk.
Yup. The original statement was dangerous FUD which should be urgently corrected.
Needing to be familiar with all the special cases (like the VERY special case of x.y.name which I previously knew nothing about) kind of ruins everything and introduces yet more security risk.
I'm sorry, what ? Admit ? Confusion ?
In the case of .co.uk it has been around since 1996. HN is a technical forum, most people here should be well aware it is a serious SLD. I honestly can't believe it even needs clarifying.
Hell, if you use AWS Route 53 you'll see they use co.uk as one of their nameserver suffixes[1].
[1] https://docs.aws.amazon.com/Route53/latest/DeveloperGuide/SO...