Cannot comment but if the question is asked of QP I am sure they will advise. The grades etc shoudn't be secret (another of my gripes when I was there) but who knows how they treat them now. I worked on the new grades but that was some years ago (pre-1996) and they may have been amended since then.
I could find out if QP don't respond. I may even still have the working papers from 1996.

All jobs are graded using the company JE plan (taking into account numerous weighted factors including, accountability for supervision, budgetary responsibility) and yes the grades do affect salary and some (but not all) allowances as some grades are "banded" for allowance purposes. The personal grade is ordinarily the same as the job grade but this isn't guaranteed so make sure that the two are the same.