Vilified for their dark arts since the phone-hacking scandal, Britain's popular press won a victory this week after prosecutors acknowledged that the long-held practice of paying sources for stories was legitimate.

The Crown Prosecution Service (CPS) on Friday dropped cases against nine journalists facing trial for illegally paying police and other public officials for information, while another four were cleared in court.

At the same time, the CPS issued new guidelines making clear that journalists should not always be prosecuted for paying for scoops.

"It is simply obvious that there are circumstances in which it can be in the public interest for journalists to pay for information," a former head of the CPS, Ken Macdonald, told BBC radio on Saturday.

A total of 29 journalists have been prosecuted under the £20-million (28-million-euro, $30-million) police investigation into illegal payments to officials, codenamed Operation Elveden.

But just three have so far been convicted and only one of these verdicts looks set to be upheld.

Prosecutors have blamed the poor success rate in part on their use of a 13th-century offence, misconduct in public office, that is very hard to prove.

But Macdonald said that "not enough weight was attached to the public interest in free expression and the freedom of the press, and that was an error".

- 'Witch-hunt' -

Paying for stories has long been common in the British media, and many of the journalists prosecuted said they had no idea they might have been committing a crime.

Their defence teams relied on the argument that it was in the public interest to obtain and publish the information.

Britain's top-selling newspaper, The Sun, has said there was a "witch-hunt" against its journalists and in a front page Saturday condemned the "Crown Persecution Service".

Its associate editor Trevor Kavanagh led calls for all outstanding cases against journalists to be dropped, saying: "It's time to call off (the) dogs."

The Sun's royal editor, Duncan Larcombe -- himself cleared in an illegal payments trial last month -- said Operation Elveden was "an affront to a democratic country".

Meanwhile Bob Satchwell, executive director of the Society of Editors, which represents journalists, said the probe was an "incredible fiasco".

- Disgrace of hacking scandal -

Operation Elveden was launched in 2011, during public outrage over the tactics of the British tabloid press following the phone-hacking scandal.

Revelations that reporters had illegally accessed the voicemails of hundreds of public figures, including a murdered schoolgirl, prompted Rupert Murdoch to close down his News of the World tabloid in disgrace.

Both his newspaper empire, News International, which also publishes The Sun, and Trinity Mirror, which owns the rival Daily Mirror and Sunday Mirror tabloids, have since paid out millions of pounds to hacking victims.

News International also handed over reams of emails and documents to the police, which formed the basis for their investigation into allegedly corrupt payments to officials.

Former News of the World editors Rebekah Brooks, who rose to become Murdoch's right-hand woman, and Andy Coulson, later Prime Minister David Cameron's director of communications, were both prosecuted and both cleared.

By contrast, 21 public officials have been convicted, people the CPS said were "motivated by greed and self-interest".

The new guidelines make clear that officials who break the public's trust will continue to be prosecuted.

Brooks was also cleared of phone-hacking following a lengthy, high-profile trial, although Coulson was found guilty and sentenced to 18 months in jail.

The scandal sparked the creation of the Leveson inquiry into the culture and practices of the British press, which recommended in 2012 that a new system replace the existing regime under which the press regulate themselves.

However, most of the main newspapers have refused to accept the new system, instead setting up their own self-regulation body to which they now refer complaints.