There are so many slight variations that they are almost impossible to keep a track of. When I did my first degree it was at a college (formerly RAF Padgate), which was overseen by the University of Manchester. All the BA degrees were Ordinary because they all entailed joint studies and the University of Manchester (more correctly titled the Victoria University of Manchester) would not issue Hons to joint studies. As such, my degree was issued as a pure BA without any possibility of Honours. It was all a bit odd at a time when many Higher Ed establishments were offering Joint Honours degrees.
Having completed the degree I applied to undertake an MSc in one of the subjects and was accepted subject to achieving the appropriate grade - a Distinction. This was equivalent, they felt, to a 2:1 or better in an Hons degree. I have to say that I didn't ever feel that others on the MSc, who had come from 'proper' universities had enjoyed a better standard of preparation than I had.
There are people starting to come through the system now with MSci degrees but no Bachelor credentials - these are 4-yr courses where the end result is an MSc, but by skipping the BSc bit, it allows the courses to be funded (by loan) for the full period; the extra 'i' is the tell-tale.
Having been in the mob now for 29 years, there are still times when I fall back on things I learned (especially stats!) and I do use the post nominals on business cards and the like. In my view it's the correct thing to do.
Incidentally, I still hold the view that the post noms act as a form of warning to others of how much professional knowledge can be expected as from a particular JO. As a very new flt lt 'Green Shielder', the fg offs around me were often a lot more professionally experienced than me.
STH MSc BA RAF