The rear bushes are so constrained by the suspension geometry that even when they are completely ruined, there is no detectable play on the MoT. You can feel a definite improvement in the handling of the rear when they are replaced though
They seem to fail with age more than mileage, the main problem being the rubber bushing delaminates from the alloy housing which is what causes the creak. The rubber is rotating in the housing, rather than twisting.