Normal subdomains are just created by the owners of the truncated domain name you mention. If a site lets people use subdomains, you would have to take it up with the site that gives them out.
Indeed, untracable unless the subdomain seller provides their own WHOIS. I would say it makes subdomains more difficult to hijack as the contact details of the owner are irretracable, if the subdomain provider is stable then (like .uk.com or .eu.com) then you probably do a very good deal if the price is right and if you care about security.
You could try going to www.123-reg.co.uk type in the name as if you are checking to see if it is available - when it comes up taken just click the whois to view owner details.(if they have'nt chosen to keep them private)
they do - uk.com - eu.com - web.com and a few more.
The caveat on the whois of subdomains is that if it is a centralnic domain (The usual suspect, web.com etc.) , their whois services are notoriously out of date and incorrect (The "famed" web.com sales of yester-year still show the names as with their "original owner" and expired ).
Stay away from the fake TLD's, and any subdomain being used as a subdomain will be owned by the owner of the domain itself, typically.
If you want to post the domain for a more definitive answer, please do.
-Allan :gl: