Virgin Media's traffic management and my old cable modem

I've banged on about Virgin in the past and how they have great bandwidth when it works but terrible customer communication and technical support.
They recently introduced a traffic management system that ramps down your bandwidth when you've spanked the connection (that you paid for) between 16:00 and midnight. What they didn't tell anyone was that if you're an old Telewest customer the model of cable modem you have (Scientific Atlanta WebStar if you're wondering) isn't compatible with the traffic management system (it's all done using a QOS protocol that only recent-model modems support).
Now I know why iPlayer, YouTube etc. wouldn't work every evening (much to the annoyance of the kids) - I was getting only 150Kbits per sec, not 20Mbits! Hopefully the new cable modem will solve this.