Members of the public and journalists will be banned from seeing the contents of secret documents on the Cabinet and Royal Family under measures quietly announced by Gordon Brown last week.
The Prime Minister's reforms on improving parliament contained a little-noticed plan to block Freedom of Information requests on Cabinet papers, even if there is a public interest case.
The blanket exemption, which will be seen as a retrograde step in access to information and transparency, also applies to documents relating to members of the Royal Family.
The publication of Cabinet papers and Royal Family documents are currently subject to a 30-year-rule. Anyone can use an FOI request, in the public interest, to ask for the documents to be published within those 30 years. Requests can be blocked by a ministerial veto – as was the case in the demand for Cabinet minutes of discussions in the run-up to the Iraq war. But FOI requests for Royal papers have been successful.
The change ends the public interest FOI option, however, and a blanket exemption is in place to "protect constitutional conventions".
A commission set up by Mr Brown and headed by Daily Mail editor Paul Dacre recommended reducing the current 30-year-rule to 15. Mr Brown has decided on a 20-year-rule, which was announced last week. All documents will be released under the 20-year-rule.
Graham Smith, of the anti-monarchy campaign Republic, said: "We have been successfully using freedom of information to raise questions about Royal use of public funds and resources and to question [Prince] Andrew's role as trade ambassador. It appears they would prefer to remain in secrecy, and that begs the question why?"