what is your provider selling?
www.u-k.org (one single hostname) this is normally not possible.
.u-k.org (a normal domain, like microsoft.com, yahoo.com, ...) You can create any subdomain like mail.u-k.org www.u-k.org, ftp.u-k.org and so on
.yourname.u-k.org (like amazon.co.uk)
Normally for org domains, the only valid option would be *.u-k.org and it seem a good choice for a non-profit organisation located un the uk (but the name doesn't giva any information about the organisation).
After visiting the site, the only option available to you is *.yourname.u-k.org
The company is making big profits, since there are no registry fees for the subdomains (the company pays for u-k.org and can create any number of subdomains). They remain the owner of the domain and can kick you out of business if they like!!! It looks like you could 'register' your own 'domain', but in fact you only get a subdomain, and subdomains carry no rights.
It's like i would sell one of my subdomains: would you like something like yourname.verfaillie.com or yourname.idemdito.org?
(i sell them for 10 pounds too, my paypal account is firstname.lastname@example.org )