Will definatly fail on MOT, Check your bushes and linkages and the dog bones found underneath the bike, If not any of those is your shocker adjustable? make sure someone hasnt slackened it all the way, what happened with the rox?
When my bike failed it's MOT it says "exsessive play/extra movement in rear bushes" so it could possibly be that.. And when you say "it lifts more" you mean once you've gotten it lifted so suspension is completly open, you have like an extra inch of lifting upwards "away" from the swingarm? (when u lift the swingarm stays but the frame/bike lifts?) im pretty sure it wont be the underlinks if the swingarm moves with the bike when you lift it, it'll be your bushes or the spring is too loose