No, they are in effect subdomains - these certainly should not be confused with proper TLD's like .com, .net, .org etc
There are a whole hosst of them:
To name just a few.
Basically the company owns "uk.com" and they are willing to sell you a subdomain of it "mysite.uk.com"
You can treat it as a seperate domain, have e-mail and further subdomains if you like.
However the bottom line is it's still just a subdomain and it is debateable if even "good names" will ever be worth anything.