No, you haven't missed anything, OzEx, the UK used to have a very clear sytem, which is the one I referred to, called MSA for Minimum Safe Altitude. The trouble is, the book that defined that has now been withdrawn and MSA now only has the meaning of Minimum Sector Altitude (i.e. the 25nm circle).
We want to use the old system, which suited our operations (low level, off airways) and I guess we still could, but there's no authoritative reference for it any more. I should say (because pPruners are so quick on the draw!) that there's no reference that I'm aware of. The new reference we have, in JAROPS, I've already described.