Hi BoneYardFarm,
I would not doubt your terrible experiences with the Tribunal service for one moment and I am really sorry that it happened that way for you.
However, for the sake of our members who are thinking of going down that route, many people do have a reasonable experience. I can assure that the DWP do not challenge all decisions which do not go in their favour.
I was at a Tribunal hearing last week and my client had been able to get an additional bit of evidence - a letter from her GP requesting that the Panel awarded her PIP and giving reasons. She got this just a couple of days before the hearing so we took it with us. I passed it to the Court Official who greeted us in the waiting room asking if we could submit it. She then asked the Judge who agreed, and two copies were taken, one for the Judge and one for the DWP presenting officer who was there.
I know this does not dilute your terrible experience, but I just wanted to say that yours was in my experience an unusually bad one, and in my experience not typical.
Best wishes
Catherine
Nothing on this board constitutes legal advice - always consult a professional about specific problems 
