Enough already.
I hate the current environment where the student makes a mistake, the examiner watches (gives enough rope) to the student to see if a correction is made. When no correction is made the exam is not passed. Wrong says the student 'you can't do that!'.
But no, now the student is always right and the examiner doesn't know what they are doing and therefore the only recourse is to legal action for some dreampt up reason such as 'defamation'.
You screwed up the test, the CAA were, IMHO, gracious enough to waive the re-test fees. The examiner treated you how they felt you required to be treated on the day. Flying around with the wrong QNH, irrespective of parallax, which I personally think is a weak excuse, is a fail. Pure simple.
The world and the job owe you nothing, far, far better people have made mistakes, taken it on the chin and got on with it. What makes you so special.
Take responsibility for your own actions, the 'defamation' for failing a CPL check ride will be nothing next to the damage your reputation will take for taking the CAA to court over this childish tantrum. The aviation world is very small from a professional point of view and names get very well known. The airlines all talk to the CAA and such stupid cases are often a talking point over a coffee or around the water fountain. Just a word of caution you understand.
Unless you can categorically prove, as in Luke Skytoddlers case, that you set the correct QNH and not the wrong one then the Examiner is in the right and you are in the wrong. Unfortunately for you there is no external agency that can confirm you set the correct altimeter setting therefore you are in the wrong.
Welcome to life.
P.S. Please don't ever try an I.R.
