The process of transferring a .UK domain name from another registrar is different when compared to other domain extensions. In case of a .UK domain name, the transfer needs to be commenced with the current domain registrar.
So firstly initiate the transfer with the registrar that you currently have your .UK domain name with. You need to provide an IPS Tag to initiate the transfer and you may need to contact the current registrars support department to see how this can be done. The IPS Tag to provide is PDR-IN.
After this is completed then procced to transfer the domain via our Website here.