PaddyB - as an ex BT person myself I have just encountered exactly the same problem. Only difference is one premises with two billing accounts. The old account had Fibre 2 + BT TV + email. The new account has Fibre 100 only.
Successfully got both billing accounts showing under My BT ID . The problem is that once toggling to the new billing account even though it shows the Billing details if you try showing the Products it keeps defaulting back to showing the old billing account products which is now just BT email only - because Fibre 2 + BT TV both ceased out today as required.
End result is that I can't follow instructions to import my BT email account to the new billing account as per instruction pasted below and advised by Sales Support team on the phone (have also attempted on the MyBT mobile app) ...
select Your Products from the top of the page.
Then scroll down to the Included in your product section and click on the link to Import an email address.
You'll need to provide the email address and password of the email you want to move and select Enter.
If the email address is linked to another BT ID, you'll be asked to provide details of this too.
Once the move is complete, you'll get a confirmation message and the email address will be shown in your email management page.
