LONDON (REUTERS) - A former policeman and an ex-prison officer admitted on Friday to selling information to the Sun, a British tabloid newspaper owned by Rupert Murdoch, in the first guilty pleas to come out of a huge police investigation into wrongdoing by journalists.

The charges stemmed from an inquiry launched in 2011 into allegations journalists from Murdoch's now-defunct News of the World newspaper had hacked into mobile phone voicemail messages.

That inquiry was later widened to include other activities, including payments to public officials for stories.

The long-running scandal forced the closure of the News of the World and has called into question the judgment of British Prime Minister David Cameron, who was friends with several of Murdoch's senior executives.

Former police officer Alan Tierney pleaded guilty on Friday to two counts of misconduct in public office for selling stories to the Sun about the mother of England soccer player John Terry and about Rolling Stones member Ronnie Wood.

Ex-prison officer Richard Trunkfield pleaded guilty to misconduct in public office for selling information about a high-profile prisoner.

In separate cases on Friday, Rebekah Brooks, the former head of Murdoch's News International British newspaper arm, appeared in court and the case in relation to her was adjourned to a later date.

Andy Coulson, an ex-News of the World editor and Cameron's former spokesman, and Clive Goodman, a former News of the World reporter, also appeared and the cases in relation to them were adjourned.

John Kay, the Sun's chief reporter, pleaded not guilty to an offence of conspiracy to commit misconduct in public office.