We've done this several times and will be doing it again this year.
Our only problem was with my travel agent (not Virgin) who seemed determined to make me take the insurance and almost failed to get me my tickets in time.
Since then I've always asked them to put a note on my booking that I do not want to take the insurance.
If you book on the phone or with an agent, they will try to tell you that, but if you do it online, there is no way they can add on any charge for NOT taking the car.