On the rare occasions I have used this service I have connected with my BT id and the password I use to log into my account at BT.com. Several years ago the "Indian" help desk changed my id to be the same as my primary email address but I have kept separate passwords. Having failed to connect to a BT hotspot 4 times in the last week I have now discovered that using my email password connects.
Can someone point me to the definitive BT definition of a BT Id? Years ago it had nothing to do with email addresses but since then I've seen BT web pages with "normally the same" "should be the same" "the same as" etc.
It is recommended by BT that your BTID and password should be the same as your "main" email address and password. This, in their mind, allows you to manage all your BT services and products in one place and using only one username and password. They don't seem to get the folly and security issues regarding this but that is another story.
It is possible to have your BTID password and your BTMail password to be different if you wish.
BTWifi was initially accessed by the BT Broadband account holder's "Primary/Main" email address and password. This was then changed to be accessed by the account holder's BTID and password, which if you did as BT suggested, would be your main email account and password.
There appears to be a problem with the BTWifi and BTID synchronisation of passwords and it is often the case that when you change one of the passwords it is not matched on the other.
Basically the whole idea of a BTID and its working has been a mess since day one and continues to still be a mess.