If you haven't read this Guardian report (and yes, I did contribute) then please do.
There's not a shadow of a doubt the Prince's tax arrangements are in the box marked "PR" because they sure as heck aren't related to any tax law I can find.
Even if he does pay income tax on the Duchy's income (and it's never been clear to me that such arrangements accord with any recognised tax law) he does not pay capital gains tax on its gains and nor will his estate pay inheritance tax on the value of his life interest which would both seem appropriate in tax trust law. So, this looks decidedly like tax from the Starbuck's PR book, but not from the statute book.
And the right question is, why is that?