You don't have or have the option to have an alias Jo.
For Blueyonder (ex-telewest) you have mailboxes.
jb12k4567 would be your first mailbox/internet user name. jb12k4567 is also the primary e-mail address, now because this is difficult to remember and a bit of a mouthful to give out to anyone. You can add an alias to that mailbox, so you could give it the alias jo.bloggs.
So mails sent to jo.bloggs would go to the mailbox jb12k4567.
Hope this helps.
I'm guessing you are ex-ntl? So you have no need to make a alias. You can just make more e-mail address.
This link should take you to the right place