When you purchase a domain through Nominet your contact details are added to the domain registrar's database. This database can be queried by anyone using a search that is commonly referred to as a whois lookup, and an example website to do this from is our Gradwell Status Network Tools page. If you enter gradwell.co.uk into the Host to lookup search box on that website you'll find information on the registrant (in this case, Gradwell), including who to get in touch with if you have queries about the domain.
Non-trading entities who have registered use of a Nominet domain (usually ending .uk) have the option to "opt out" of having their address details returned when a query on their domain is made. For the criteria for requesting this opt out please read this Nominet article.
If you wish to change your WHOIS status, please contact our customer support team, who will be able to make the change for you.