BP measurement is a black art when it comes to measurement of borderline cases. It's very hard for me to comment on this situation as I don't know a) the particulars of it and b) the extent to which AMEs are able to go to assess your BP, before having to revoke your medical and refer you on for further assessment.
I can, however, well understand your frustration. Certainly, I would never take such a drastic decision on a single BP reading taken at the beginning of a consultation. It's important to get the patient at their ease and where there is doubt about the BP value and it is important, I generally get them to lie down in a quiet examination room for ten to 15 minutes and read the paper to relax, before retaking the BP.
QDM