Actor Hugh Grant has warned any "further compromise" by government ministers over press regulation would be a "betrayal of the promises" made to media abuse victims.
He said the British Government was "terrified of the press" and was doing all it could "to oblige the press barons".
On Tuesday, Britain's Culture Secretary Maria Miller said newspapers' proposals for regulation had been rejected.
But she suggested the Government was willing to consider some of the ideas put forward by publishers.
Mr Grant, a member of the Hacked Off campaign, accused senior Tories of an "abuse of democracy" by trying to "sabotage" plans for a royal charter agreed by all parties in Parliament.
The report of the Leveson Inquiry into press standards recommended a tougher form of self-regulation backed by legislation, and Mr Grant said any suggestion such a system would limit free speech was "propaganda on the part of the press".
He said some of the main newspaper groups "refuse to accept any system which would make them accountable for any of their actions".
Mr Grant said Lord Leveson had made "very mild" recommendations but the press was determined to "mark its own homework".
He said victims of press abuse, such as the families of Madeleine McCann and Milly Dowler, had been told by David Cameron that new rules would protect people from the press.
"Any further compromise would be a betrayal of the promises made by the secretary of state and above all by the prime minister to them," Mr Grant added.
Bob Satchwell, executive director of the Society of Editors, said Ms Miller was simply talking about "tidying up" press regulation plans.
He said the minister agreed with Lord Leveson that a regulation system forced on the press without its consent would be "unworkable".
On Tuesday Ms Miller announced that the Privy Council - an ancient body which advises the Queen, mostly made up of senior politicians - had rejected press proposals for a royal charter.
She referred to principles in the Leveson report such as independence and access to arbitration and said an alternative plan would now be "improved", adding that ministers were said to be willing to consider some of the industry's ideas.