The central bargain of Westminster democracy is that the monarch stays out of politics, and in exchange they get to stay in the role, both legally and literally. Prince Charles - already famous for his undemocratic interventions in politics - is apparently planning to tear up that bargain:
Prince Charles is ready to reshape the monarch’s role when he becomes king and make “heartfelt interventions” in national life in contrast to the Queen’s taciturn discretion on public affairs, his allies have said.
In signs of an emerging strategy that could risk carrying over the controversy about his alleged meddling in politics into his kingship, sources close to the heir say he is set to continue to express concerns and ask questions about issues that matter to him, such as the future of farming and the environment, partly because he believes he has a duty to relay public opinion to those in power.
“He will be true to his beliefs and contributions,” said a well-placed source who has known him for many years. “Rather than a complete reinvention to become a monarch in the mould of his mother, the strategy will be to try and continue with his heartfelt interventions, albeit checking each for tone and content to ensure it does not damage the monarchy. Speeches will have to pass the following test: would it seem odd because the Queen wouldn’t have said it or would it seem dangerous?”
But any political comment by an unelected monarch is, by definition, dangerous. The idea of an unelected monarch purporting to tell elected Ministers what to do even more so. If a future king Charles keeps doing that, then Parliament will have to rethink the role of the monarch, and whether they want them to have any constitutional role at all.
As for New Zealand, I think its unlikely that Charles would pay any attention to us (though now I'm curious: has he sent any of his infamous "black spider memos" to any NZ Minister?) But the idea of a monarch who purported to be able to tell us what to do would not sit well with our democracy. If there was any suggestion that he would, then it would be time to rid ourselves of that piece of historical baggage.