Wheel judder at Speed

[Multispacer]

Hello, I have noticed on my recently acquired B9 2008 1.6Hdi Multspace XTR that I have quite bad steering wheel judder around about the 70 MPH range. I put it down to needing wheel balancing. I recently took it to my local tyre dealer who informed me the balance of the front wheels was spot on and he couldn't fault the balancing [he didn't charge me] He also checked the tracking and that was also fine after a small tweak. I still have the judder though. Anyone else had the same symptoms? Any ideas? I was thinking maybe it could be the rear wheels out of balance causing it? Or maybe the cheap brand tyres [which wouldn't be my choice] but they all seem to be virtually brand new, so I don't really want to go out and change them until they wear out if I don't have to