As I said, the U.K. does have a two-tier system. In every Westminster system, the salaries have to be set by law. That's a statutory requirement. In Australia, I think it is one tier, also in statute. However, again in every jurisdiction, the Prime Minister has the responsibility and the opportunity to structure the cabinet in the way that he wants. There may be statutory amendments, as are presented here, that happen in those jurisdictions as well.
On October 5th, 2017. See this statement in context.