Where does the right to restrict it's use come from? And I was not referring to tartans that were designed by chiefs of clan members. I'm pretty much talking about pre-existing tartans.
Think of it this way: the Duke of Argyll does NOT recognise the "Campbell of Argyll" tartan as a bona fide Campbell tartan, yet many people the world over wear it. No restriction per se, but no recognition. It's the Duke's perogative as Chief to do so. The so-called "Black MacMillian" tartan is a similar tartan with no recognition from the Chief.

T.