I'm an IR PhD, and I lecture undergrads and MAs too. Our uni also offers internal PhD funding. As far as my uni goes, even if you get a Masters, its unlikely you'll get a funded PhD (if that's what you want), even if its just a fee waiver... the competitions too strong. Plus, when I was doing my MA there were a small number of students who got 2:2s and were signed up to do the PG diploma, and if their marks were enough they were upgraded to the MA. None of them managed it.
Sorry to sound negative, but this is just my experience!