I’ve been abroad for a short while and now find that I am locked out of my btinternet.com email account for security reasons. How can I resolve this issue please? There seems to be no relevant option when I call 0800 800150.
If you are locked out of your email account for "security reasons" you will need to change your email account's password.
You can do that by either usng the "forgot log in details" link on the BTMail log on page or by going into your MyBT and going to "Your Products" then "Email, manage" the click on the relevant email account and follow the prompts for changing the password.
https://www.bt.com/help/email/email-security/how-can-i-tell-if-my-email-account-is-no-longer-secure