Britain's newspapers vowed to scrutinise a deal struck by politicians on a tough new press regulator, which they warn threatens 318 years of press freedom.
MPs insisted the agreement would rein in misdeeds exposed by the News of the World phone-hacking scandal without curbing press freedom, but newspapers said the government had "crossed the Rubicon".
Prime Minister David Cameron said the new regulator would have the power to issue harsh sanctions on misbehaving newspapers, including fines of up to £1 million ($1.5 million, 1.16 million euros).
"We need a system of tough, independent self-regulation that will deliver for victims," he told parliament.
Cameron warned that regulation of Britain's famously unruly press must "actually deliver" for victims of media intrusion, rather than being simply "an exercise in grandstanding".
The new body will be able to force newspapers to issue upfront apologies for inaccurate or intrusive stories, Cameron said, as well as offering a free arbitration system for victims.
Newspapers that refuse to sign up for the voluntary system could face extremely high "exemplary" damages in court cases.
A statement issued by the Daily Mail Group, Telegraph Media Group and News International -- publishers of The Sun and Times newspapers -- said they needed "time to study" before formulating a response to the "deeply contentious issues" contained within the plan.
Political leaders said the deal, finally struck at 2:30 am (0230 GMT) after months of negotiations, addressed the abuses laid bare in last year's Leveson Inquiry into media ethics, without bringing an end to more than three centuries of press freedom in Britain.
However, the Daily Telegraph accused MPs of "crossing the Rubicon".
"Last night, parliament decided that 318 years was long enough to let newspapers and magazines remain beyond its influence," said its editorial.
Cameron set up the inquiry in the wake of revelations that Rupert Murdoch's News of the World tabloid illegally accessed the voicemail messages of a murdered schoolgirl as well as dozens of public figures.
Over eight months of hearings, Judge Brian Leveson heard testimony from dozens of victims of press intrusion, including actor Hugh Grant and Harry Potter author J.K Rowling, as well as politicians, journalists and newspaper executives.
Leveson concluded in his final report that British newspapers had "wreaked havoc with the lives of innocent people" and recommended a complete overhaul of their system of self-regulation, backed by a new law.
The governing coalition had been split over how to implement Leveson's recommendations, with Conservative leader Cameron rejecting plans for a new press law advocated by his Liberal Democrat coalition partners and the opposition Labour Party.
The compromise reached early Monday will see a new press watchdog created under a royal charter, a special document used to establish organisations such as the Bank of England and the BBC.
The charter will be protected by a separate law which, while making no mention of the press, will state that all charters passed after March 1, 2013 can only be modified by a two-thirds parliamentary majority.
Both sides claimed victory on Monday, with Cameron saying he had saved newspapers from potential censorship, and Labour leader Ed Miliband saying the new system would be protected in statute from meddling politicians.
Cameron insisted the new charter did not amount to a law regulating the press.
"It's wrong to create a vehicle whereby politicians could more easily in the future impose obligations on the press," he told lawmakers.
Miliband said newspapers had "nothing to fear", after the owners of the Daily Mail, The Sun and The Daily Telegraph earlier warned they may boycott the new regulator if it is written into law.
Hacked Off, the campaign group representing victims of media intrusion, said the proposals were "second best" to a full press law but would help prevent a repeat of the scandal.
The new system "will protect the freedom of the press and at the same time, protect the public from the kind of abuses that made the Leveson Inquiry necessary", said Brian Cathcart, one of the group's founders.
But free speech campaigners Index on Censorship warned that Monday's deal spelled a "sad day for press freedom in the UK".