You had better be prepared for some disappointment. The options for complete account management of blueyonder addresses was removed some time ago when VM integrated the mail systems of its predecessor organisations.
This is the current position:
If these "alias" addresses are linked to secondary blueyonder accounts you can delete them yourself in My Virginmedia but to do this you need to delete the secondary account they are attached to. The aliases share the same mailbox and password as the secondary account they are attached to.
If they are linked to what is now the primary blueyonder account you cannot delete them because to do so would be to delete the primary account which you cannot do.
Now this is a serious warning. VM have said that they will look at removing "alias" address from primary accounts. My view is that you would be ill-advised to ask them to do this. The last one of these I saw lead to complete disaster. VM managed to delete the primary account (somehow, and heaven knows how or even what they did) and it was the devil of a job for them to get it back into working condition.
You can work out for yourself what is the best way forward.
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