The problem is that, in the UK, the procedure for a 'fail' debrief is clearly laid down. If you go against that you are leaving yourself wide open to litigation. A clever lawyer could say to the examiner "So if you were so certain that you saw a 20kt speed error, why did you have to ask him to confirm it contrary to CAA Document 24?". I have known this happen in an appeal to the CAA but the CAA backed the TRE. They did however insist on the TRE having more training prior to a check with a CAA Inspector. An Industrial Tribunal Judge might not take the same view, and might side with the candidate.
I agree that, having given the result, it is important to send the candidate away with confidence, knowing that, with extra training, they can achieve the required standard.
Airclues