Running down M6 yesterday, pulling a very small lightly loaded trailer, with not excessive weight (200kg tops) in car......... plus me & wife, our 54 plate D4D tourer began jumping out of top gear whilst under acceleration. It would stay in top under deceleration/overun (or if I kept pressure on the stick), & no other gears were affected. No advanced warning, no difficulty changing gears, no funny noises or vibrations.........