So, after all this time, just what will Prince Charles's letters reveal?

Great excitement in royal-watching circles as the possibly looney tunes letters of Prince Charles are set to be published tomorrow, according to a report in the Guardian. The newspaper has spearheaded the decade-long Freedom Of Information battle to get the scrawled missives released.

The establishment fought to keep secret Charles's “particularly frank” letters to British government ministers, amid fears the letters could undermine his political neutrality.

The Guardian reports the letters will finally be published on tomorrow.

The 27 letters were sent between Charles and ministers in seven government departments in 2004 and 2005 and were the subject of a Freedom of Information Act request by the Guardian journalist Rob Evans.

The government has been battling to protect the Prince of Wales from scrutiny over what the former attorney general Dominic Grieve has described as Charles’s “particularly frank” interventions on public policy in the letters.Grieve vetoed the information tribunal’s original decision to order publication in 2012, warning that the letters “contain remarks about public affairs which would in my view, if revealed, have had a material effect upon the willingness of the government to engage in correspondence with the Prince of Wales, and would potentially have undermined his position of political neutrality.”

The letters will be published with some redactions tomorrow.

In March, supreme court judges finally approved the publication of the letters. David Cameron said at the time that the decision was “deeply disappointing”.

The letters were sent between the prince and seven different Whitehall departments that at the time were led by Labour secretaries of state. They were business, innovation and skills; health; children, schools and families; environment, food and rural affairs; culture, media and sport; the Northern Ireland Office and the Cabinet Office.There is now an “absolute exemption” on all FOI requests relating to the Queen and the heir to the throne.