Prince Charles has secretly placed aides in key roles in Whitehall departments linked to his principal interests, without the knowledge of government ministers, it has emerged.
The Prince has been able to install at least three employees in government departments responsible for drawing up policies that could impinge on his business and political interests.
One member of Charles's staff spent two years at the Cabinet Office, while another spent 14 months on a rural policy team at the Department for the Environment, Food and Rural Affairs (Defra).
Ministers spoke of their shock and anger at not having been informed.
One minister complained that the placements raised "questions that need to be answered about who agreed it".
"I think it's undemocratic," the minister said.
"It raises questions about whether Prince Charles is exceeding his position as a constitutional monarch in waiting," the minister added. "There is a question about what they are doing and whether they are influencing policy."
Paul Farrelly, Labour MP for Newcastle-under-Lyme, said he would raise the matter with ministers.
"It raises constitutional questions about the influence the monarch in waiting has over policy and there will be questions in the house when it returns," said Farrelly.
Secondments between government departments, businesses and charities are relatively common, but are meant to be transparent.
However, neither the government nor the Prince's office would provide further details of the appointments.
The Prince's office refused to identify the three employees it had placed in civil service roles, or to disclose what duties they had carried out. It also declined to reveal who had authorised the placements.
A spokesman for the Prince said the secondments were arranged on an "ad hoc" basis.
"All three secondments were suggested on the basis of professional development and the paperwork was arranged by the relevant HR departments," the spokesman said.
It is thought to be the first time in modern history that a member of the royal household has been seconded into government.
One member of Charles's staff dispatched to Defra in January 2012 worked in a rural policy team, the Sunday Times reported.
Defra declined to disclose what areas Charles's aide worked on or whether ministers were told.
"It's complete and utter news to me," said one former Defra minister.
Charles has made public his support for a cull of badgers, a policy which falls within Defra's remit. He has also said he opposes building houses on the green belt, and is against GM crops.
The Prince also has commercial interests through the Duchy of Cornwall, which earned him £19 million last year. Defra said Charles's employee "would not have been involved" in issues affecting the duchy.
A "junior official" from Charles's staff was seconded to the Cabinet Office to work on "community-based things" such as David Cameron's flagship "big society" concept. She is believed to have worked under civil society minister Nick Hurd, whose brief includes organisations such as the Prince's Trust youth charity.
Another employee is understood to have spent six weeks working inside the Cabinet Office.
The Queen had no staff working in government in any similar arrangement, Buckingham Palace confirmed.
Charles has previously been accused of using his position to lobby for changes to the law.
The civil service posts would be the first suggestion that Charles exerts influence on policy from within government.
Deputy Prime Minister Nick Clegg was not informed of the Whitehall placements, said sources close to Clegg.