In order to transfer a .uk .co.uk etc domain to us, you must first update the domains IPS TAG
This can be done with the existing registrar.
Change the IPS TAG to: EXTEND
Once this is done, you can proceed to transfer the domain to us by searching for it in our domain search and locating it at the bottom/transfer section of results.
http://www.vari.host/domain-names/
If you have any problems, please submit a support ticket for assistance.