IT'S SOLVED!!!.... after months of the same issue being intermittent, and multiple visits to different garages... I finally got a warning light which game them the answer (there isn't an emoji good enough for this... !)....
SOooo... there is a speed sensor that is attached to the gearbox which was causing the issue (even when idling - so its not just about "speed") - anyway VW wanted c£600 inc labour to get in there and do it... but its done....
Hopefully that will help others as I have gone months with the same issue and no warning lights, soo frustrating...