Had car up in the air again, checking for rear brake drag, bent suspension or damaged bushes but all seemed ok. Rear toe also checked with drive-over gauge and same both sides. Had a thought to swap tyres left to right (had already moved fronts to rear but on same side) just in case. Hey presto - problem solved. So, I have a tyre with a high rolling resistance now on right side which appears to balance out any camber effects. Tyres are original Continentals with 5k+ miles only and have been very carefully inspected for damage etc. and all checked multiple times with digital and manual tyre pressure gauges. So, don't do as I did. Swap your tyres diagonally to eliminate any possibility.