I found the following posted by a moderator:-
BT Email
As yet I could not find the bit about returning customers but I will keep looking.
Yes, you'll be able to link it to your new broadband account. You can only do this once your broadband has been set up and activated.
We'll send you confirmation of your broadband activation, and once you get this you can follow the advice to Move an email address (mailbox).
If you're moving a Basic email address, we'll automatically upgrade your email to Standard.
If you're moving a Premium email address to your broadband account we’ll automatically close the Premium account when the last email address is moved.
Can I move my BT Email address to another account? | BT Help
Thank you everybody for your contributions. this morning I phoned up BT, I was passed up the chain till I eventually got to speak to a manager. I was informed that my problem in not being able to manage my email accounts was down to a software conflict between the EE software and BT's. It is a know problem that affect a small proportion of customers, the engineers are working on it. So it's a matter of waiting. I feel I have ascended up the chain of command as far as possible, the next step would be the software engineers. It is a matter of waiting now.
But just a big thank you for all the contributions of advice, it's very much appreciated.
Thank you. Brian.