Simple and good question. Rather more complicated answer.
Why do you want to do this. Spam avoidance?
Is this BY address your primary e-mail address? That is the one you use to log into MY Virginmedia?
OK - if the answer to the second question is "yes" then you can never get rid of the address. It is yours for as long as you have a VM account. You will always need it for logging into My Virginmedia for account management.
However if it is a secondary address you can delete it. You can also create new virginmedia.com addresses but you cannot move your BY e-mail into the new address.