Just as an update - after contacting Virgins CEO and appraising him of my problems, I am pleased to say the UBRS for my area was re-balanced and since midweek everything has been flying. Still going to the 50mb in November as I'm sure it will be ok now.
I should note that I found all the technical staff I contacted to be pleasant and trying to be helpful, but, it's very hard to get past the first line phone support folk, who on the whole don't have the expertise or clout to get the more technical things sorted out if it's a problem at Virgins end.
Still this noisy wheel got oiled, and to anyone else with similar problems I would advise letting those higher up (politely) know of your difficulties.