Parallax error on an altimeter?!! Give me a break.
If that is your excuse, then you obviously don't have much of a professional career ahead of you my friend. The examiner wasn't born yesterday, I guarantee you he will have known exactly what was set on the altimeters. It was the wrong QNH, that is a fail. Deal with it.
A little bit worrying that a few people are saying it's ok, it was only 1 mb. Where do you draw the line here, 3/4 mb's? 10 feet below minima, it's only 10 feet or maybe 20 feet, it's okay
You are being tested for a professional licence, there should be no error on altimeter settings, and if mis-set, should be picked up timeously which clearly is not the case here.
TP offers sound advice which, if I were you, take heed and get this crazy notion out of your head.
Playing silly games trying to get one over on the CAA will only backfire and bite you on the proverbial.