Why Is It Slightly Misleading to Describe the British Constitution

Why is it slightly misleading to describe the British constitution as unwritten?

A) Most of it is written down, but not in a single place or document.
B) It exists as one single, written document.
C) Unwritten implies that it is ambiguous and poorly understood when it is in fact clear and unambiguous.
D) It is so well understood that it is perhaps more definite and defined than a written constitution.