According to the rules of the .co.uk and .be domains, it is not allowed to modify the holder from the control panel. A special process is needed:
Case 1:
If you wish to modify the holder of the .co.uk you must access the website of the entity that owns the registration of these domains which is: Nominet
Case 2:
In the case of domains .be, you must send an email to the company in which it is registered, indicating the change to be made, as this process must be carried out manually by the company.