I had another play around with it this morning and whilst I think I've configured it correctly the Traffic on Route button is greyed out. I have tried inputting a destination thinking that maybe this will work. Admittedly I have yet to set off on a journey. The TMC stations it picks up in the Yorkshire area are Classic FM and Real radio. Incidentally, I have found more info on how the service operates here for those wanting a more technical explanation...
http://www.m5board.com/vbulletin/archive/index.php/t-57465