John, you say that the vehicle has been fitted with new discs ?. If the hubs were not thoroughly cleaned before the discs were fitted, this can cause your vibration. The fault is almost certainly an imbalance in the hubs etc. You need to have the wheels balanced on the vehicle. There must be someone who can do this surely ??.
Certainly the discs were fitted very recently (mechanic owner) and I have to say there's absolutely no sign of judder or imbalance there.......at 45 MPH, hands off, the steering wheel is juddering away merrily - brakes on and there's no difference at all
Still a bit confused!
John