To show your email folders go to your View menu, then click on Folder Pane and select Normal. Your email folder list should reappear.
If it does not you may have set Outlook up as a POP3 account instead of an IMAP account. POP3 does not replicate the folders in webmail where as IMAP does.
If you have set it up as a POP3 account you can not change to IMAP on the fly, you would need to delete the POP3 account and then set up your email account as an IMAP account.
Before doing that check that all the emails that you want are still on the BT email servers by checking in webmail.
