In that case, there may be an error in configuration, as Thunderbird only reports whatever is returned from server.

I cannot login to jandcward@btinternet.com and my other btinternet account from Thunderbirds.The error is an incorrect password but it is correct

Hey, I had the same issue before! It might be worth checking if you've enabled 'Less secure apps' in your BT account settings or trying to re-enter the password after removing it from Thunderbird's saved passwords. You could also try logging into your BT account through the web to make sure there’s no security block or new verification process. Hope that helps!