Britain's Prince Charles has been receiving confidential government papers for decades.
The 67-year-old royal has had access to information intended only for the Cabinet, and Bernard Jenkin - the chair of the Commons constitutional committee - has argued ministers should have been more open about the controversial scenario.
He told BBC Radio 4's Today programme: "Obviously it would have much better if they would have been open on this point.
"They publish the Cabinet manual in which it might have been perfectly reasonable to make this clear, that these documents go to the heir of the throne."
The Cabinet Office spent three years fighting a freedom of information battle to keep its so-called "precedent book" secret - a move that has subsequently been criticised by the Conservative Party MP.
He said: "I imagine the precedent book itself contains precedents that are security sensitive, which are secret and should not be disclosed, and that is why in principle the precedent book has been protected.
"But this is the civil service in transition still from the period of secrecy to the period of freedom of information where they're still not used to drawing a line between what is secret and what is not secret."