Seems that you do need a superhub. I queried it in the Virgin forums and they sent me the superhub FOC. That came last week. I'm on BB L so had

I called 150, option 5 then 2, today as my UBR was showing that the upgrade was available -
http://apcyberax.co.uk/myubr.php
They checked, clicked something at their end, the superhub lit up like a Christmas tree, then rebooted - yay, I now get
Note: If your UBR does not show the upgrade is available then it's a waste of time asking VM to look at your account.
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Virgin Cable (L)