There is something important here for history buffs. the power of the Magna Carta arose because even Kings found it expedient to reissue it to remind those powerful enough to usurp the king's power that a rule actually existed to live under.
It was from this repetition that the whole concept of a binding rule of law arose and embedded itself in even the popular mind. Parliament was not too far behind that idea.
Sometimes it is not the law itself but the historic context that is important. After all men can gather and establish rules of conduct and men can gather to modify those rules. It is still what give those laws meaning that matters. The Magna Carta laid out procedure that all thought that they could ignore but it was ultimately time honored procedure that ruled in the end.