British Prime Minister David Cameron abandoned cross-party talks on press regulation on Thursday as police for the first time arrested a current national newspaper editor over phone-hacking. Conservative Party leader Cameron said lawmakers would vote on his proposals for a new newspaper watchdog on Monday after he failed to reach a deal with his Liberal Democrat coalition junior partners and the Labour opposition. Labour and the Lib Dems want statutory regulation as recommended by the Leveson Inquiry, which Cameron commissioned after the hacking scandal at Rupert Murdoch's now defunct News of the World tabloid. But Cameron told a hastily arranged press conference after the talks broke down that such a move could curb press freedom, and accused his opponents of "hijacking" parliamentary time on the issue. "Statutory regulation is not necessary to enforce the Leveson principles," Cameron said. "It is wrong to cross that rubicon by writing key elements of press regulations into the law of the land." Cameron said he would instead ask lawmakers to vote on Monday on his plans for a Royal Charter -- a special document used to establish organisations including the BBC and the Bank of England. The move is a big gamble as he will struggle to get his plans through parliament in Monday's vote, a further blow for a prime minister struggling with a weak economy and divisions in his party. Labour leader Ed Miliband said Cameron had made a "historic mistake" and failed to serve the needs of hacking victims as he had promised to. Brian Cathcart, director of the campaign group Hacked Off, accused Cameron of an "astonishing betrayal" of victims of press abuse. The hacking scandal had dramatically widened just minutes before Cameron's press conference as police said they had arrested four journalists from the Trinity Mirror group, one of Murdoch's rivals. James Scott, the editor of weekly tabloid The People, and his deputy Nick Buckley were arrested in dawn raids on their homes on Thursday, along with the Sunday Mirror tabloid's former editor Tina Weaver and her former deputy Mark Thomas. Scotland Yard said detectives "have identified and are investigating a suspected conspiracy to intercept telephone voicemails at Mirror Group Newspapers". The new investigation focused on a period between 2003 and 2004 at the Sunday Mirror. Police said the alleged crimes were "a separate conspiracy" to the investigations into phone-hacking and the bribery of public officials at News International, the British newspaper arm of Murdoch's News Corporation empire. Trinity Mirror told AFP: "We are cooperating with the police and we have no further comment to make at this stage." Prosecutors said separately they had charged a former policeman with misconduct in a public office for allegedly selling information to Murdoch's daily tabloid The Sun. It is alleged that James Bowes, 30, an ex-sergeant, sold details about three "high profile investigations" to the tabloid in 2010 and was paid £500, the Crown Prosecution Service said. Around 100 people have been arrested under various phone-hacking and corruption investigations sparked by the scandal at the News of the World, which shut down in disgrace in July 2011. Several people have been charged including Cameron's former media chief Andy Coulson and former News International chief Rebekah Brooks. Coulson and Brooks had both previously edited the News of the World. Cameron launched a judicial inquiry into press ethics led by judge Brian Leveson days after the closure of the News of the World. The tabloid was closed after it emerged it had hacked the mobile phone voicemails of hundreds of celebrities, politicians and ordinary people. In his conclusions last year, Leveson called for a new, tougher independent regulatory body backed by legislation.