Since the new email format has gone live it will not autofill my email user name. I have to type it in every time.
Autofill is a function of your browser. The url has changed you will need to save the new details.
The autofill is a feature of your browser not BT.
Go into your browsers settings and go to the Saved Passwords and check to see if your BT username and passwords are stored. If they are, find the one that is stored for your BT email account and delete it. You should then be offered to save it again the next time you are logging on.