If you go into wireless then Mac filtering it seems to work on mine, only full time though you can't select time ranges. Obviously Virgin don't care as this box has been around a few years now and there not done anything about it.
I sent an email to the VirginmedaiCEO Tom Mockridge over the weekend. Today I was contacted me by someone in his Exec team who refered in turn to someone in the engineering team. In short his response was that "Virginmedia do not support MAC filtering or blocking" .
I have asked to have my HUB 3 replaced with a Super HUB 2AC on which I now MAC filtering does work.