Dr Gordon Ramsay, the author of the report and a research fellow at the thinktank, said: "It is startling to see the lack of diversity of viewpoints in the Leveson coverage, not just in opinion pieces, but also from sources in news articles.It is also striking that, while expressing a clear view of their own, few papers gave the public the information necessary to make their own minds up about the future system of regulation.
Its study found that negative coverage of the judicial inquiry "increased drastically" in the 100 days before the report was published, with articles in this period five times as likely to contain only negative viewpoints as only positive ones.
The tabloids were the most hostile: 34 out of 43 articles in those titles were found to be "negative only" by the researchers, compared with 62 out of 85 reports published by broadsheet newspapers, in the 100 days before publication.
The critical articles were "overt and visceral" containing "strident language" that generally warned that Leveson's report would lead to political control of the press, the study shows.
"However, the data gathered here shows that, where press coverage has expressed a view on the Leveson Inquiry, one viewpoint has dominated. Though much of the coverage of the inquiry during the public hearings was neutral, comment and opinion pieces were overwhelmingly negative.