If you have PR, the majority of Scottish voters would have to vote for secessionists for Scotland to secede.
Similarly, if you had PR, the majority of UK voters would have to vote to leave the EU (hopefully on the basis of some sort of plan put forward at the election) to get Brexit.
It's an indirect way of doing it, but in my view a much better way. I simply disagree with referenda in principle. (You don't have to concur by the way.) Cameron made a massive blunder offering one, and only did so because he thought he knew the answer he would get. He was wrong. And no one serious did any planning to prepare for a "Leave" outcome, because no one serious expected it to happen. I doubt (very much) that even Boris Johnson expected to get "Leave" or that he gave a single thought to how he would implement it if he did win. He was playing a game. And (in my view) he still is. And it's all about him. He's laughing either way, because a) he's loaded and b) he will now get a fat pension and Police protection for life. Please don't tell me this is any way to run a country. It's a massive clusterfuck, and there is now no happy ending, no matter what happens as a large proportion of the population are going to be seriously pissed off, Brexit or no Brexit.