Three former senior journalists from Rupert Murdoch's British tabloid the News of the World have pleaded guilty to charges relating to phone-hacking, the trial of two of the media mogul's former editors heard on Wednesday.

Rebekah Brooks, Murdoch's former British newspaper chief and Prime Minister David Cameron's ex-media head Andy Coulson are on trial at London's Old Bailey court accused of conspiring to illegally access voicemail messages on mobile phones, charges they deny.

The court was told on Wednesday that ex-chief correspondent Neville Thurlbeck, former assistant news editor James Weatherup, and ex-news editor Greg Miskiw had pleaded guilty to conspiracy to intercept communications at earlier hearings.

Their guilty pleas, which had not previously been reportable, are the first public admissions by former News of the World journalists since police launched an inquiry in 2011 into allegations that staff on the Murdoch paper had hacked the phones of celebrities, politicians and victims of crime.