Any question answered...

http://www.tartansauthority.com/tartan/the-growth-of-tartan/royal-tartans/

Tradition has it that those who have no tartan of their own can wear the Black Watch (The Universal or Government Tartan) or the Hunting Stewart, but not the Royal Stewart without the express authority of the Queen. However, commercialisation in recent times has rather blurred this. The one tartan which cannot be worn by anyone unless the Queen's permission has been granted is the Balmoral.

Guess it depends on the context.