The Duke of Cambridge sometimes receives copies of confidential Cabinet documents, it has been reported.
William sees such papers “occasionally”, according to the BBC.
The report follows the disclosure in an official document released after a lengthy freedom of information battle that the Prince of Wales has been routinely receiving copies of confidential Cabinet papers.
The Cabinet Office’s “Precedent Book”, drawn up in 1992, says the documents of the Cabinet and ministerial committees are provided to a “standard circulation” list limited to the Queen, the Prince of Wales and government ministers.
Heirs to the throne are believed to have been included in the group since the 1930s.
The book warns that the need for secrecy is so great that “special care in circulation and handling” is required, and Cabinet ministers are handed their copies in person.
Four chapters from the book were released to campaign group Republic after the Cabinet Office failed in a three-year effort to avoid making it public.
The BBC said it had learned that William “occasionally receives copies of confidential Cabinet documents”.
A Government spokeswoman, while not commenting on whether William receives the papers, said: “The Duke of Cambridge is a senior member of the Royal Family and future heir to the throne and therefore of course it is appropriate that he is regularly briefed on government business.”
A Kensington Palace spokesman declined to comment.
Graham Smith, chief executive of Republic, which campaigns for an elected head of state, said: “The document we got through the FOI makes no mention of Prince William or the son of the heir to the throne.
“This raises the question, why is Prince William getting the documents when there’s no reference to that requirement in the Cabinet guidelines? If this is happening who else is getting them, are they going to Prince Andrew - is Kate seeing them?
“There’s definitely a need for a lot of clarification from the Government about exactly who is seeing what, and why.”
The organisation has already written to Prime Minister David Cameron demanding that Charles be removed from the circulation list for the papers, which would include details of ministers’ discussions on upcoming legislation normally kept secret for at least 20 years.
Mr Smith said: “The disclosure of Cabinet papers to Prince Charles is quite extraordinary and completely unacceptable, not only because they would contain highly classified information but because it gives him considerable advantage in pressing his own agenda when lobbying ministers.”
The revelation about the papers follows the release earlier this year, following another FOI battle, of the so-called “black spider letters” sent by Charles to ministers over a number of years on subjects ranging from homeopathy to rainforests and defence spending.
In its letter to Mr Cameron, Republic said: “The fact that ... Charles has privileged access to Cabinet papers is a further cause for concern as it means he is able to lobby ministers in secret at every stage of policy development process.
“It is plainly wrong that Charles can lobby on new policy proposals even before the public are aware of the existence of such proposals.”
Mr Smith said the group was not raising similar concerns over the Queen’s access to the documents because of her position as head of state.
“The Queen has a constitutional function, but the Prince of Wales has none, and he is known to be lobbying on a number of issues,” said Mr Smith.
A Cabinet Office spokesman said of that: “It has been established practice for many years that the sovereign and the heir to the throne receive the minutes of Cabinet meetings. It is important that the head of state and her heir are properly briefed.”
The disclosure that Charles has been receiving the papers follows the publication earlier this year of some of his secret letters to ministers.
The documents disclosed the Prince corresponded on a range of topics from tackling the then prime minister Tony Blair over a lack of resources for the armed forces fighting in Iraq, to raising the issue of badger culling and the use of herbal medicine.
Twenty-seven letters - 10 from Charles to ministers, 14 by ministers and three letters between private secretaries - written between September 2004 and March 2005 were published.
They were released in May following a 10-year campaign by Guardian newspaper journalist Rob Evans to see the documents following a freedom of information request.
Charles faced criticism that he was lobbying ministers about issues but Clarence House defended the Prince’s decision to write the letters.
A spokesman said at the time: “The publication of private letters can only inhibit his ability to express the concerns and suggestions which have been put to him in the course of his travels and meetings.’’
A further batch of letters was released in June and showed the Prince wrote to ministers about the benefits of complementary medicine, the need for affordable rural homes and the threat to heritage buildings.