I can confirm that it is NOT available to all loyal customers. See my post re having to leave Virgin Mobile.
If I try to avail of the double data I get the following message. I called up and just got a blank refusal.
"Sorry, we can't make any more changes to your tariff at the moment.This is because you've asked for a tariff change recently. If you've made a change and wish to cancel it, please call us on 789 from your Virgin Mobile phone or 0345 6000 789* from any other phone and we'll do our best to help. *Please note standard charges apply. Please check with your network operator for rates."