Crucially, he declared, the “full Leveson” of statutory regulation would fail because newspapers would refuse to co-operate.
He added: “Let me stress again, if you have a system that people do not take part in then you have not actually solved the problem.” A Labour spokesman said: “The PM’s decision is very disappointing. We still hope for an agreement. We still believe there can be an agreement.”
The reaction from Mr Clegg’s circle was angry. “We are surprised and disappointed about what has happened this morning,” said a party source.
“Until then we thought we were making real progress and inching towards a deal.
“On a conference call this morning between the three leaders, the Prime Minister unilaterally decided to pull the plug on the talks. This has come out of the blue.”
Pressure group Hacked Off, which backs statutory controls, claimed its staff were “escorted out” of the Department for Culture when Mr Cameron suddenly pulled the plug mid-way through a meeting with civil servants.
Labour MP Ben Bradshaw called it “a gross betrayal of victims and craven surrender to perpetrators”.
It is unclear whether Mr Clegg will tell his MPs to vote with Labour to defeat the Tory proposals. “Nothing has been agreed in government,” said the Lib-Dem source.
One possible outcome to Monday’s votes is that MPs will vote down both the full Leveson proposals and Mr Cameron’s watered-down version.
That would leave the scandal of press misconduct still unsolved after months of wrangling.