A former UK journalist has admitted illegally accessing celebrities’ voicemail messages while working at Rupert Murdoch’s News of the World tabloid and its rival, the Sunday Mirror.

Dan Evans, 38, is the fourth News of the World journalist to plead guilty to phone hacking while working at the disgraced tabloid, but the first reporter to admit that he used the illegal practice at the rival Sunday Mirror.

His guilty plea was revealed in Britain’s phone-hacking trial at London’s Old Bailey court on Monday as he appeared as a prosecution witness at the high-profile trial of former News of the World editors Rebekah Brooks and Andy Coulson and several other former Murdoch executives.

Asked by a prosecutor what his job at the Sunday Mirror was, Evans said: “I was a news reporter. Principally I was tasked with covering news events, investigations, undercover work – latterly with hacking people’s voicemail.”

He claimed he was recruited by the News of the World from its rival in 2005 partly because of his phone-hacking skills.

The seven people on trial at the Old Bailey all deny charges linked to hacking between 2000 and 2006.

Australian-born media tycoon Murdoch shut down the News of the World in July 2011 following a storm of revelations that its staff had hacked the phone of a murdered schoolgirl as well as hundreds of celebrities and public figures.

Earlier on Monday, British actor Jude Law gave evidence, saying the media seemed to have an “unhealthy amount of information” about his private life.

The 41-year-old – the most high-profile celebrity to testify at the trial so far – was also confronted for the first time with claims that a family member sold stories about him to the paper.

He told the court he was aware that a relative gave information to the tabloid, which was famed for its celebrity scoops, but had never heard suggestions that they were paid.

Law said he had been under intense media scrutiny between about 2001, following his nomination for an Oscar for The Talented Mr Ripley, and 2005 or 2006, a period in which he dated actress Sienna Miller.

“There seemed to be an unhealthy amount of information that people, or someone, had that meant they had access to my life and my whereabouts,” Law said.

Wearing a grey suit, white shirt and blue spotted tie, he described how he was followed by “packs of photographers” who always seemed to know his movements.

“I became aware that I was also turning up at places having arranged to go there secretly… and the media were already there,” he said.