Newspapers chose not to print details of John Whittingdale's relationship with a sex worker because withholding the story would allow them to "influence his position" as culture secretary, a Hacked Off campaigner has claimed.
Evan Harris, a former Liberal Democrat MP, told Channel 4 News on Wednesday that Whittingdale did not want to fully implement the second part of the Leveson inquiry because of his connection with the press.
The executive director for Hacked Off said that the newspapers who knew of Whittingdale's relationship with an escort publish similar stories "week in, week out".
Harris said that the decision not to print a similar story about the secretary of state "was not because of a new-found interest in ethics".
His allegation was slammed for being "spurious" and one "that people can't substantiate".
Harris said: "It is not about whether those three newspapers ought to or ought not to have published that story.
"Those are the Mail on Sunday, The People and The Sun. There may or may not have been public interest justifications... generally we would say that those newspapers would be right not to publish that story on its own.
"But the fact is that week in, week out they do publish those stories.
"And The Independent found that the reason they didn't was not due to a new-found interest in ethics, but it was because they thought they could influence his (Whittingdale's) position.
"And his position has changed."
Harris added: "The Prime Minister said that we will go ahead with Leveson part two... and John Whittingdale said it will take place.
"The Dowler family were promised it will take place. Now the line is it might take place."
Damian Collins, who is on the Commons select committee for Culture, Media and Sport, said it was wrong for such accusations to be made without any proof.
The Tory MP said: "I think that is wrong and I think that today we have seen a lot of people insinuating things that they can't prove, exploiting someone's personal circumstances - in many ways exhibiting many of the qualities they are so critical of the newspapers for exhibiting.
"There is no evidence that John Whittingdale has been influenced about this at all.
"His position as secretary of state and the government's position has been clear on this and we have made progress on implementing Leveson's recommendations."
Harris conceded that "there is no proof".
This point was seized upon by many viewers, including presenter Cathy Newman after the show.
Addressing the allegation that Whittingdale did not want to fully implement Leveson because of his connection with the press, Collins said: "It is one that is a completely spurious allegation that people can't substantiate.
"And I think it is wrong for it to be thrown around in this way.
"He (Whittingdale) has made progress on implementing Leveson."
Earlier today, BBC political presenter Andrew Neil skewered Harris for similar claims he made on the 'Daily Politics' programme.
Neil repeatedly asked what evidence there was to suggest Whittingdale had effectively blocked the second part of the Leveson inquiry to please newspapers, and prevent them printing details about his private life that surfaced late last night.
But Harris failed four times to provide proof for the claims, and eventually admitted he might be wrong.