Prince Charles's letters to ministers to be published
Secret letters sent by the Prince of Wales to Labour government ministers a decade ago are to be published later.
The 27 "black spider memos", so called because of Prince Charles's handwriting, will be released after a decade-long campaign by The Guardian.
The government's veto on publication was declared unlawful by the Court of Appeal last year - a decision which was upheld by the Supreme Court in March.
The letters, written in 2004 and 2005, will be published with redactions.
Their publication follows a ruling on Tuesday by the Upper Tribunal of Britain's Administrative Appeals Chamber.
It said the material could be published subject to any "provisional redactions" to protect personal data of people other than the prince.
The letters, which cover the period between September 2004 and April 2005, reflect - according to former attorney general Dominic Grieve - Prince Charles's "most deeply held personal views and beliefs".
During a visit to a Prince's Trust charitable project in London, the prince was asked by a reporter if he was "worried" about the release of the documents.
"Very predictable," he replied, as his press secretary Kristina Kyriacou pushed away the microphone of Channel 4 News reporter Michael Crick.
BBC royal correspondent Peter Hunt
In public - in speeches, on television and through articles - Prince Charles has, for decades, attempted to influence public opinion on matters that he cares passionately about.
But how does he behave in private?
It's a question officials, particularly at Buckingham Palace, would rather wasn't being asked.
It's a question we'll be in a better position to answer with the publication of these letters sent to members of Tony Blair's government.
They'll be examined for evidence of any pressure brought to bear by a hereditary monarch-in-waiting on elected ministers, and for any evidence that government policy was changed following the prince's intervention.
The correspondence may prove to be benign or may lead people to conclude the future king has been in the habit of overstepping the mark.
The prince's letters were sent to a number of government departments while Mr Blair was prime minister.
They are known as "black spider" memos because of his distinctive handwriting and use of underlining and exclamation marks.
Denis MacShane, a Labour former Europe minister, saw some of the letters - written on large foolscap paper with heavy black ink - during his time at the Foreign Office.
He said that at the time the letters he saw were seen as interesting but were not taken very seriously by staff at the Foreign Office.
He told BBC Radio 4's Today programme: "The problem is no member of the Royal Family will ever dare to write a letter to the government again for fear their private views will be front page news.
"I think he should be able to communicate with the government privately."
In 2005 Guardian journalist Rob Evans originally applied to see the Prince's letters under the Freedom of Information Act 2000 (FOI). This was initially denied by the information commissioner and several legal decisions followed.
Writing in the Guardian, the journalist said his paper limited the request to cover just eight months because FOI rules allow applications to be refused if too much information is requested.
In 2010, the Freedom of Information Act was tightened and now correspondence involving the monarch or heir to the throne cannot be made public for 20 years or five years after the writer's death, whichever is longer.
Mr Grieve vetoed an original decision to order publication made by the Upper Tribunal in 2012, but it was eventually ruled that his actions were invalid, paving the way for the documents finally to be disclosed.
The documents are expected to be published by the Guardian, the Information Commissioner and the Cabinet Office at 16:00 BST.
In March, Prime Minister David Cameron called the Supreme Court judgement to allow publication "disappointing".