They became known as the "black spider memos" – letters written by Prince Charles in his near indecipherable handwriting and sent to government ministers, marked "private and confidential", containing his views on the government's environment policy.
But the Attorney General, Dominic Grieve, has used a rare ministerial veto to block publication of the letters, overturning the decision made by three judges at a Freedom of Information tribunal.
The 30 letters written between 1 September 2004 and 1 April 2005 represent, according to Mr Grieve, the Prince's "most deeply held personal views and beliefs" and "are in many cases particularly frank". Consequently, their publication could "damage… the Prince of Wales's political neutrality" and "seriously undermine the Prince's ability to fulfil his duties when he becomes King".
"The Sovereign cannot be seen to favour one political party above another, or to engage in political controversy," Mr Grieve said, in a 10-page document explaining his decision. "Any such perception would be seriously damaging to his role as future monarch, because if he forfeits his position of political neutrality as heir to the throne, he cannot easily recover it when he is King."
The details of the 30 letters remain unknown, but Mr Grieve makes clear that 27 of them fall under the terms of the Environmental Information Regulations 2004, which grants the public the right to know about decisions, policies and activities that affect the environment.
The Prince's Duchy of Cornwall estate has been leasing waters for farming oysters in Cornwall.
Land on the Crown Estate has also been leased for wind farms, despite the Prince having spoken against them, before changing his mind. Mr Grieve said there was "nothing improper in the nature or the content of the letters" and that the Prince had a right to confidential correspondence with ministers.
There are those, however, who suggest it is the writing of the letters, not their possible publication, that undermines the Prince's neutrality.
"He's an important person, so he should accept that these are public-domain documents," said the Labour MP Denis MacShane.
In 2010, Prince Charles told NBC he was "born into this position for a purpose", claiming: "I don't want my grandchildren or yours to come and say: 'Why the hell didn't you come and do something about this?'"
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