David Cameron has failed to keep his "solemn promises" on tackling press standards, according to victims of media intrusion.
In an open letter on press regulation, a number of signatories including Gerry and Kate McCann - who have received libel damages over false stories linked to their daughter Madeleine's disappearance in 2007 - said that the Prime Minister is at risk of "betraying" the public.
The letter, published in the Guardian, calls on Mr Cameron to "honour" his promises to implement a system of press regulation that has "real teeth".
Mr McCann told the newspaper: "Feelings are very strong among those of us to whom the Prime Minister publicly and privately made his pledges.
"If he does not keep his promises to implement the cross-party agreement in full, allow the Leveson Inquiry to be completed and put the needs of the public before press proprietors, we will have been betrayed by him."
The Government was accused of reneging on the recommendations of the Leveson Inquiry after Culture Secretary John Whittingdale announced last year that he was considering scrapping plans, which had been part of a cross-party agreement, to force newspapers to pay court costs in libel and privacy cases, whether they win or lose.
The signatories of the letter - who also include relatives of people who died at Hillsborough, victims of the 7/7 terror attacks and Christopher Jefferies, who was wrongly accused of the murder of Joanna Yeates - have said the Mr Cameron has refused to meet them over the issue of whether a second part of the Leveson Inquiry will take place.
They accuse him instead of meeting regularly with newspaper proprietors, including the owner of The Sun and The Times Rupert Murdoch and his editors "on no fewer than seven occasions" between June and December 2015.
Their letter states: "We believe that it is not just us whom you are at risk of betraying, but Parliament, the public at large and the future victims of a press industry which was condemned by Leveson for 'wreaking havoc in the lives of innocent people'.
"If your promises are not kept, history tells us that newspapers will wreak that havoc again.
"It is not too late. Please honour your promises."
In 2014, the McCanns won £55,000 in libel damages from the Sunday Times over a story which suggested that they had kept evidence from authorities investigating their daughter's disappearance.