The supreme court will rule on Thursday on whether highly sensitive secret correspondence between Prince Charles and government ministers should at last be released in the public interest.
The ruling by Britain’s most senior judges will be the climax of a 10-year legal battle between the Guardian and Whitehall for access to the heir-to-the-throne’s so-called “black spider memos”, which are what an information tribunal described as “advocacy correspondence”.
The tussle over the right to see 27 letters written in 2004 and 2005 between Charles and ministers in seven departments in Tony Blair’s government began with a freedom of information request in 2005, but has since involved 16 judges ranging from an obscure tribunal to the highest court in the land.
The former attorney general, Dominic Grieve, blocked the release of the memos in 2012, saying that to publish them could “seriously damage” Charles’s kingship. Grieve said the correspondence contains the prince’s “most deeply held personal views and beliefs” and disclosure might undermine his “position of political neutrality”.
The court will rule on whether Grieve was right to use his veto. If it sides with the Guardian to uphold the original information tribunal decision to allow publication, it would be the first successful use of the Freedom of Information Act to obtain the prince’s official correspondence with ministers and the first successful challenge of an attorney general’s veto of an independent court.
If released, the letters could provide fresh ammunition to the prince’s critics, including republicans, who argue that someone who is known to have privately lobbied ministers and disagreed with government policy on issues ranging from farming practices to complementary medicine, can never successfully unify the nation as monarch.
The monarchy’s own website states that “the system of constitutional monarchy bridges the discontinuity of party politics,” but if the letters show him attacking Labour policies, he risks being seen as part of that discontinuity, critics said.
“Charles may be seen as running against public opinion in a serious way and highlighting issues that are not based on good science,” said the Labour MP Paul Flynn, who is a member of the Commons political and constitutional reform committee. “The Queen has been a successful monarch for a very long time because her mouth has been bandaged against any indiscretions and that is the role of the monarch.”
If the judges rule in favour of continued secrecy, it will be a significant victory for the prince who strongly defends his right to talk privately to ministers. It will also be a relief for the government, which has spent at least £275,000 on lawyers to fight the legal battle.
Patrick Holden, a farmer and friend of the prince’s, said: “The Guardian is doing the public a disservice by campaigning for the release of these letters. It is the right of the Prince of Wales to have private correspondence with ministers and it is entirely appropriate.”
In the past Charles has stirred controversy by lobbying politicians over issues such as the genetic modification of crops, but aides have often stressed that he grasps the need to drop his “advocacy” role when king.
Last autumn, however, his allies told a Guardian investigation into the shape of his future reign that he intends to continue to make “heartfelt interventions” in public life after he becomes sovereign, in contrast to the Queen’s taciturn discretion on public affairs.
The courtroom jousting started in late summer 2010 in front of three judges who sat on a freedom of information tribunal. In strict legal terms, the prince has not been part of the case because it was the government that was fighting to keep the correspondence secret. His lawyers, however, could be seen in the tribunal keeping an eye on the arguments.
Sir Stephen Lamport, the prince’s former private secretary, and the veteran Whitehall mandarin Sir Alex Allan, were called to give evidence in favour of keeping the letters secret, but they failed to persuade the three tribunal judges, who ordered the letters to be published in September 2012.
Key to their decision was their conclusion that the prince was trying to change rather than learn about government policies.
“The essential reason is that it will generally be in the overall public interest for there to be transparency as to how and when Prince Charles seeks to influence government,” they decided.
A month later, Grieve issued his veto.
The dispute moved to the high court when the Guardian sought to show that Grieve had acted unlawfully. Three high court judges sided with Grieve in 2013, but in March last year Lord Dyson, the leading civil judge in England and Wales, and two colleagues came down in favour of the Guardian.
Ministers were not prepared to give up the fight and allow the letters to be published. They hired a new legal team and took their case to the supreme court in November.
Even if the supreme court rules in favour of releasing the memos it will not open the floodgates to Charles’ correspondence with ministers, who have tightened up the Freedom of Information Act to impose a blanket ban on the publication of any correspondence involving the monarch or the heir to the throne for 20 years, or five years after their death, whichever is longer.
Ministers conceded that they had made a mistake when Tony Blair’s government originally passed the Act in 2000, because it permitted the disclosure of the prince’s letters if it was shown to be in the public interest. The ban was dubbed “the Prince Charles amendment” by one MP, implemented, according to Whitehall sources, following pressure from the royal family.
