The investigator at the heart of Britain’s phone-hacking scandal said yesterday he acted on orders from the News of the World, casting doubt on claims by Rupert Murdoch’s empire that he was a rogue operator.

Private detective Glenn Mulcaire broke his silence as a British parliamentary committee said it had ordered Mr Murdoch’s son and heir apparent James to give written clarification of answers he gave on the scandal last week.

The scandal has dragged in police and politicians and spread to the United States and Australia, but increasingly it has returned to the question of how much key figures within News Corp. knew about hacking at the tabloid.

In a statement issued by his lawyers, Mr Mulcaire, who along with former NotW royal editor Clive Goodman was jailed for hacking in 2007, expressed “sincere regret”, but added that he was “effectively employed” by the paper from 2002.

“As an employee he acted on the instructions of others,” the statement said. “Any suggestion that he acted in such matters unilaterally is untrue.”

He spoke a day after the mother of a murdered eight-year-old girl said police had confirmed her details were found among his papers. Claims that he hacked the phone of a murdered 13-year-old ignited the scandal earlier this month. Rebekah Brooks, editor of the News of the World from 2000-2003, and her successor until 2007, Andy Coulson, have both denied authorising any phone hacking or knowing that the practice was being used by their staff.

Ms Brooks and Mr Coulson, who went on to become Prime Minister David Cameron’s media chief until January this year, have since been arrested.

James and Rupert Murdoch, along with Ms Brooks, who quit as chief executive officer of News Corp.’s British newspaper wing News International earlier this month, answered questions from Parliament’s media committee on July 19.

Committee chairman John Whittingdale said yesterday that he would be writing to James Murdoch about his testimony to the committee.

Meanwhile a protester who splattered Rupert Murdoch with a foam pie when the media mogul was testifying to the same committee pleaded guilty at a court in London to assault and harassment.

The 26-year-old Jonathan May-Bowles, a comedian who goes by the stage name of Jonnie Marbles, pleaded guilty at City of Westminster Magistrates court in London to assault and to causing harassment, alarm or distress.

Leaving court, May-Bowles echoed Australian-born Murdoch’s own statement to the committee, telling reporters: “This has been the most humble day of my life.”

The judge warned Mr May-Bowles that he faces jail when he is sentenced on August 2.