The Lib Dems Deputy Leader Simon Hughes told ITV1's The Agenda that he is opposed to the statutory regulation of the press.
He told ITV News Political Editor Tom Bradby: "There must be a strong argument for making sure we don't have a dominant force which runs all the channels so we don't have the choice, they influence too much and set the prices, set the agenda."
"There is the other issue which is about regulation... I'm not for having a statutory system but I am for having a system that says look there will be a fall-back."
Lord Justice Leveson's report is published on Thursday.
The Agenda is on ITV1 at 10.35pm and at 11:35pm in Scotland.
Mayor of London Boris Johnson told ITV News, during a visit to India, that he did not "think it would be right to come up with statutory legislation" ahead of the publication of Lord Justice Leveson's report into press standards.
He added: "You need to have a free press to have a free society. If you want to keep the gutters of public life clean you need a gutter press."
The newspaper claimed he would back a new, tougher model of self-regulation to replace the Press Complaints Commission - but with the threat that a statutory system could be brought in later if matters do not improve.
Former Assistant Commissioner Bob Quick told the Leveson Enquiry that he had wanted John Yates' phone records to be seized in 2007. This was part of the investigation into allegations that details of the cash-for-honours investigation were being leaked by the Met.
Mr Quick alleged that Mr Yates - who was then Assistant Commissioner - had refused to give permission, saying that he was "very well connected".
When I questioned this remark, he emphasised: 'No, Bob, I'm very well-connected' ... I didn't place huge significance on it at the time. I thought it was a bit of theatre.
On the basis of his reaction, Mr Quick alleges that Met deputy commissioner Sir Paul Stephenson decided not to investigate the phone records.