Glenn Mulcaire, who was jailed in 2007 for voicemail interceptionCopyright: Steve Parsons/PA
A statement issued to the Guardian by Mulcaire's lawyer said that the investigator was "effectively employed" by the News of the World from 2002 until 2007 and that "any suggestion that he acted in such matters unilaterally is untrue".
The statement adds: "As he accepted when he pleaded guilty in 2007, to charges of phone interception, he admits that his role did include phone hacking.
"There were also occasions when he understood his instructions were from those who genuinely wished to assist in solving crimes.
"Any suggestion that he acted in such matters unilaterally is untrue. In the light of the ongoing police investigation, he cannot say any more."
Mulcaire's statement follows the revelation that the phone number of Sara Payne, whose daughter Sarah was murdered in 2000 by convicted paedophile Roy Whiting, was found among documents confiscated from the private investigator by the Met police in 2006.
Payne worked closely with the News of the World following her daughter's death, especially with former editor Rebekah Brooks, who spearheaded the newspaper's "Sarah's Law" campaign for tighter restrictions on convicted paedophiles.
Brooks, who gave Payne a mobile phone for the purposes of the campaign, said yesterday that she found the idea that Payne's phone was hacked into by the News of the World "beyond comprehension".
Mulcaire, who was arrested in 2006 and served six months in prison for voicemail interception, issued a statement earlier this month in which he apologised for his actions, blaiming a "relentless pressure" and "constant demand for results" while working for the News of the World.