The primary registrar for the .uk domains (including .co.uk, .org.uk, etc.) is Nominet. Their system contains the actual, up-to-date details for these domains.
Before you can change the Whois for your .uk domain, you need to first check if the information in our system is in sync with Nominet. You can do this at the whois section of the following site:
You can log in to your Nominet account and manage your UK domain by requesting a password to be sent at your domain\'s administrative email via the URL:
https://secure.nominet.org.uk/auth/access-your-account.html
If the information there matches the information that you see in the joomla site User Area -> My Accounts -> scroll to Domains -> Manage (next to the domain), this means that the details for the domain in our system are already in sync with the registrar. Then you will be able to update the details via our User Area directly. Note that you won\'t be able to change the registrant name and organization. These can be changed only directly with Nominet.
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destination source:https://www.siteground.com/kb/how_to_update_the_whois_information_for_a_uk_domain/