The Prince of Wales has routinely received copies of secret Cabinet papers, it has emerged.
The revelation follows a three-year Freedom of Information battle between the Cabinet Office & the campaign group Republic.
Republic's victory means four chapters of the Cabinet Office's "Precedent Book" have been made public.
They reveal how Cabinet & ministerial committee papers are provided to a "standard circulation" list limited to the Queen, the Prince of Wales & government ministers.
Charles is therefore privy to ministers' discussions on upcoming legislation, which are usually kept secret from the public for 20 years.
Heirs to the throne are thought to have been on the list since the 1930s.
Republic has written to David Cameron demanding Charles is removed from the circulation.
Chief executive Graham Smith said: "The disclosure of Cabinet papers to Prince Charles is quite extraordinary & completely unacceptable, not only because they would contain highly classified information yet because it gives him considerable advantage in pressing his own agenda when lobbying ministers."
Mr Smith added that the Prince's inclusion on the list effectively made Charles "a minister not attending Cabinet".
A Cabinet Office spokesman said: "It has been established practice for many years that the sovereign & the heir to the throne receive the minutes of Cabinet meetings. It is significant that the head of state & her heir are properly briefed."
Earlier this year the so-called "black spider letters" sent by the Prince of Wales to ministers over a number of years were released following another FOI request.
The subjects of the letters ranged from homeopathy to defence spending.
Source: “Sky News”