The prime minister has expressed "serious concerns and misgivings" over Lord Justice Leveson's proposals for statutory underpinning to a new regulation system for the press.
David Cameron said he accepted the principle of independent regulation arguing that the current system "is badly broken and it has let down victims".
But in a statement to the Commons on 29 November 2012 he told MPs he was "wary" of legislation that had the potential to infringe free speech and the free press.
In his 2,000 page report into the culture, practices and ethics of the press, Lord Justice Leveson recommended a tougher form of self-regulation, backed by legislation, to uphold press standards, to protect the rights of victims and people bringing complaints.
Mr Cameron said the proposal for statutory underpinning would "cross the Rubicon" of writing elements of press regulation into the law, adding that Parliament should think "very, very carefully" before "leaping into this approach".
"Once you start writing a piece of legislation that backs up an independent regulator you have to write into that legislation what is its composition, what is its powers, what is its makeup, and you find pretty soon that you have a piece of law that is really a piece of press regulatory law," Mr Cameron told MPs.
He said the onus was now on the press to implement the report's proposals "and implement them radically".
Labour called the report "measured" and backed its conclusions "unequivocally".
Opposition leader Ed Miliband insisted that a new press regulator should be established in law.
He said Parliament should "put its faith" in Lord Justice Leveson's recommendations, and said he was sorry the prime minister was "not quite there".
'Workable and proportionate'
Senior Conservative MP David Davis welcomed "wholeheartedly" the prime minister's "caution" of enshrining press regulation in law.
The Conservative chair of the Commons Culture, Media and Sport Committee, John Whittingdale, said any statutory underpinning of the press needed careful consideration by Parliament.
But Labour MP Chris Bryant, a victim of phone-hacking, argued that without a change in the law "there would be more Milly Dowlers, and that will be our fault".
Liberal Democrat deputy leader Simon Hughes noted that the report said legislation was essential to underpin the independent self-regulatory system.
"'Essential' seems to be a very clear word. Do you accept that?" he asked the prime minister.
Mr Cameron said this was the "key argument" to be had about the report, and reiterated his concerns about statutory regulation.
In a separate statement to MPs, the Liberal Democrat leader and deputy PM, Nick Clegg, said he believed statutory self-regulation could be done in a "workable and proportionate way".
He said "pure self-regulation" of the press had failed for 60 years, and told MPs: "We need to get on with this without delay."
Shadow deputy prime minister Harriet Harman asked Mr Clegg if he agreed that the PM's statement "amounts to nothing more than a craven acceptance of the status quo".
Ms Harman also sought assurances the report would not be "kicked into the long grass".
Conservative MP Peter Bone said the "first duty" of the deputy PM was to "support the prime minister", and claimed Mr Clegg had "swished away" the doctrine of collective responsibility by making a separate statement.