is your business email address on your own domain, if so who hosts this for you at the moment?
If your not sure who hosts it then check your mail servers in your mail client and this will give you a good idea of who is hosting it.
if it is hosted by virgin then unless you want to continue to pay them for hosting then you will need to migrate the domain over to BT for hosting, speak to BT about this they will tell you the steps you need to go through to release the domain from virgin so they can take controll of it