LONDON (AFP) - Britain's phone-hacking scandal claimed the scalps of two top policeman as Prime Minister David Cameron on Monday cut short a trip to Africa to deal with a crisis that threatens his own position. Assistant Commissioner John Yates, who refused to reopen an investigation into the now-defunct News of the World tabloid in 2009, resigned Monday, a day after the departure of his boss Paul Stephenson, chief of London's Metropolitan Police. Yates had expressed regret last week over his earlier decision that the inquiry into the Rupert Murdoch-owned paper did not need to be revived, but pinned the blame on Murdoch's empire for failing to cooperate. "Assistant Commissioner John Yates has this afternoon indicated his intention to resign," said a Scotland Yard statement. "This has been accepted." Yates was one of the Met's most senior officers and had responsibility for special operations, but came under fire after dectectives reopened the investigation in 2011 and found thousands of alleged hacking victims. He quit when he found out he was about to be suspended. As the scandal kept scything through the heart of the British establishment, Cameron's aides announced that he would cut short a visit to South Africa and Nigeria, flying back on Tuesday evening instead of early Wednesday. They said the Conservative leader wanted to prepare a statement that he will deliver during an emergency session of parliament on Wednesday, having delayed the summer break for lawmakers for a day. Cameron has also been forced to defend his own position after Stephenson, Britain's most senior police officer, took a swipe at the prime minister's decision to hire former News of the World editor Andy Coulson as his media chief. Stephenson quit on Sunday over the force's hiring of Neil Wallis -- who was deputy to Coulson at the tabloid -- and over a spa break he accepted from a firm where Wallis was a consultant. "I don't believe the two situations are the same in any way, shape or form," Cameron told a joint news conference in Pretoria with South African President Jacob Zuma when asked about a comparison with the troubles at Scotland Yard. Coulson resigned from Downing Street in January and was arrested on July 8. Wallis was arrested on July 14. Opposition Labour Party leader Ed Miliband piled pressure on Cameron -- also facing criticism for his social contacts with Murdoch aides -- by calling on him to apologise for hiring Coulson. Asked whether Cameron should consider his position, Miliband said there was a "sharp contrast between his actions and the honourable actions of Sir Paul Stephenson who resigned over the hiring of Mr Coulson's deputy." Yates shock announcement came just hours before police bailed Rebekah Brooks - who resigned on Friday as head of Murdoch's British newspaper arm - after she was arrested on suspicion of phone-hacking and bribing police. Rebekah Brooks, former chief executive of Murdoch's British newspaper unit, News International, and editor of News of the World when it allegedly hacked a murdered girl's phone, was arrested on Sunday on suspicion of phone hacking and bribing police. Her lawyer Stephen Parkinson said she was "not guilty of any criminal offence" and that Scotland Yard would have to account for the "enormous reputational damage" to the 43-year-old -- who is a personal friend of Cameron's. He said she still planned to testify alongside the Australian-born Murdoch and his son James, who is chairman of News International, before a committee of British lawmakers on Tuesday. At a previous hearing in 2003 the flame-haired Brooks, the 10th person and most senior Murdoch aide to be arrested over the scandal, admitted the paper had made payments to police. An original police investigation into the tabloid in 2006 led to the jailing of its former royal editor and a private investigator, but it later emerged that thousands more celebrities, royals and even crime victims also had their voicemails targeted by alleged "industrial-scale" hacking. The chairman of a British parliamentary committee which grilled Yates last week over his refusal to reopen the investigation told him his evidence had been "unconvincing". Senior police officers have since faced criticism for having a series of dinners with top News of the World executives. Murdoch's US-based News Corp. is in crisis, having also had to abandon its bid for full control of pay-TV giant BSkyB and accept the resignations on Friday of Dow Jones chief Les Hinton, who had worked with the media baron for 52 years. Shares in News Corp. plummeted 5.82 percent in Australian trade on Monday.