Graham Currently you must be logged in to your xtgem account BEFORE using the links in the emails
This applies to both accounts
ie you must be logged in to your account and then use the link in the email to initiate transfer
and the receiving account must log in before using the link in their email to complete the transfer

I have requested a change so that the system allows you to login and then continue with the transfer which should be in place soon

 Graham I have just tested the changes to the transfer system and for me they are working fine
Now if you are not logged in to your account when you use the link in the email you can login and the transfer will continue