Prince Charles's 'black spider' letters set for publication after 10 year legal battle

The Royal Family’s reputation for political neutrality faces its most serious challenge in a generation as the “black spider” memos written by Prince Charles to senior ministers are finally set to published after a 10-year legal battle.

The Cabinet Office has announced that the memos would be published on Wednesday afternoon, following a Supreme Court ruling last month. Ministers had previously attempted to block their publication on the grounds that public knowledge of their contents would undermine the Prince of Wales’ “position of political neutrality”.

Their publication – which could reveal whether the heir to the throne privately lobbied government ministers on issues ranging from farming to complementary medicine – presents David Cameron with a potential constitutional crisis less than a week after the general election.

But some of the information in the letters will remain secret, after the Upper Tribunal (Administrative Appeals Chamber) approved “provisional redactions” to protect personal data of people other than Charles.

The 27 letters, given their name because of the Prince’s spidery writing, were sent to ministers in seven Whitehall departments. They were sent between 2004 and 2005 to Labour secretaries of state for business, innovation and skills; health; children, schools and families; environment, food and rural affairs; culture, media and sport; as well as the Northern Ireland Office and the Cabinet Office, and are said to contain “particularly frank” interventions on policy.

A Freedom of Information Tribunal had first ordered the publication of the memos in 2012, following requests from the Guardian newspaper. But the then attorney general Dominic Grieve took the extraordinary step of over-ruling that decision to protect the Prince’s reputation.

At the time, Mr Grieve warned they “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.”

Saying that if members of the public read the letters, they could think that the Prince had disagreed with government policy, Mr Grieve argued that disclosure would undermine the Prince’s ability to perform his duties if he became monarch.

Ministers have spent hundreds of thousands of pounds in legal fees to prevent their disclosure but, in March, the Supreme Court overturned Mr Grieve’s decision, ruling that the government had unlawfully blocked the publication of the letters.

Calling that decision “deeply disappointing”, David Cameron said it was “about the principle that senior members of the Royal Family are able to express their views to government confidentially.”

Clarence House has previously expressed disappointment “that the principle of privacy has not been upheld,” but royal aides have indicated they are relatively relaxed about the publication of the letters themselves.

The 27 documents are expected to be published by the Information Commissioner and the Cabinet Office at 3pm.