The architect of the new press self-regulation body said the industry must continue to fight state involvement "with vigour and determination".
Lord Black of Brentwood described the implications of a Royal Charter on press regulation as a "chilling prospect" in a speech to the Scottish Newspaper Society (SNS) conference in Glasgow.
The executive director of the Telegraph Media Group has overseen the development of the Independent Press Standards Organisation, which is set to replace the Press Complaints Commission in June.
The establishment of IPSO follows the phone-hacking scandal and the Leveson Inquiry into media standards.
A Royal Charter on press regulation was granted in October after the newspaper industry lost a court challenge.
Editors have argued that their alternative proposals were not properly considered.
Lord Black, speaking on The Future of Self-regulation, said: "There is a clear and present danger to press freedom in this country.
"It's vital that all the institutions which represent our industry continue to fight our corner with vigour."
The Royal Charter was a "menace" and represented an "unacceptable infringement of press freedom and freedom of expression", he said, adding: "What has happened is that politicians have laid out how they expect the regulation of the press to be organised and they now have the tools to make that compulsory if they choose to do so.
"That involvement… could easily take politicians and governments to the heart of the newsroom and what you can and cannot publish.
"That for me is an incredibly chilling, authoritarian prospect hiding behind the facade of an arcane constitutional document signed by Her Majesty the Queen.
"If ever there was a wolf in sheep's clothing – this one with a crown on it – it is this."
Lord Black said the last three years had been "the most turbulent in the history of the British press".
The phone-hacking scandal had seen a bigger police investigation than that into the Lockerbie bombing, he said, and dozens of journalists had been arrested "shamefully, in dawn raids".
He said the newspaper and magazine industry had shown an "iron resolve" during what he called a period of "intense danger and scrutiny".
More than 90 per cent of industry members have signed up to IPSO according to Lord Black, who will not feature on its board.
Independently appointed, it will have the ability to investigate "serious or systemical breakdown of ethical standards" and impose on publishers fines of up to £1 million.
A panel is expected to announce who will chair IPSO in the coming days.
Lord Black said: "It will be a wholly new organisation… not even a remote second cousin of the PCC."
The newspaper industry has launched a judicial review of the way in which its own charter drawn up in the aftermath of Leveson was rejected by the courts.
Lord Black said: "It is a legal challenge we continue to prosecute with vigour.
"Next week, on Wednesday, the issue reaches the Court of Appeal where we will have the chance again to make our case."
The Royal Charter's terms were dictated by a lobby group, with no public consultation and no vote by MPs, he said, adding: "It's for all those reasons that we as an industry should not just have nothing to do with it, but should fight it with vigour and determination."
Asked about how a national press regulator would work in the event of a Yes vote for Scottish independence, he said: "There is already a constitutional mess over the application of the charter.
"IPSO is a different kettle of fish, because it can apply throughout the whole country.
"I don't know the answer to how, if Scotland was an independent country, a regulator based in London would seek to regulate the press in an independent state.
"I guess one answer would be a sort of 'independent independent press standards organisation' which would perhaps maintain all the elements of the Editors' Code but which sought to resolve disputes in a much more local fashion.
"The answer is that it will be a matter for the industry in Scotland to decide.
"I for one think that there is, as far as media regulation is concerned, a great deal of merit in consistency and uniformity throughout the country."
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