Is 'co.uk' a top level domain? [closed]

Is the combination co.uk considered to be a top level domain, or is co.uk considered to be a subdomain of uk?

If it is the latter, is the .uk domain owned and operated by the same group that owns co.uk? This would explain why one can purchase a *.co.uk domain (or similar domains, such as *.org.uk), but domain registrars do not sell *.uk domains on their own.

The latter. .uk is a CCTLD, or Country Code Top-Level Domain; .co.uk is a subdomain thereof.

The whole of the .uk namespace is operated by Nominet Ltd.

For many years, direct registration under .uk hasn't been allowed, and the namespace has been split into the subdomains we know and love (including .co.uk, .org.uk, .net.uk, .me.uk, .parliament.uk, and so on) inside which registration was allowed (though not necessarily by everyone; some of those subdomains have very strict registration rules). But you probably ought to know that - against the wishes of many in the internet community in the UK - Nominet is opening up direct registrations in the .uk namespace as of 10 June 2014. More details can be found at http://www.nominet.org.uk/uk-domain-names/introducing-uk .