Well things aren't looking any better...
Took the wickes unit back and nipped into B+Q to buy a plasplugs jobbie. Install the disc and it runs true with no visable runout. Come to put the cover back on and the disc fouls the cover. Its like the spindle sticks too far through from the motor side. Needs a couple of washer or something between the motor and the plastic moulding.
Just hope the other one they had left isn't the same!