Glenn Mulcaire was jailed with former News of the World royal editor Clive Goodman for accessing the voicemails of public figures in January 2007.
A firmly-worded statement issued by his lawyer today stated any suggestion that he may have acted "unilaterally" was "untrue".
Mulcaire has found himself facing questions over the extent of his involvement in the saga following fresh allegations that the former Sunday tabloid illegally accessed the voicemails of murdered schoolgirl Milly Dowler, 7/7 victims' relatives and grieving military families.
Most recently, a friend of Sara Payne, the mother of murdered schoolgirl Sarah, said she was "absolutely devastated" after being told she may have been targeted by the private investigator.
Mulcaire's lawyers said: "Glenn Mulcaire has already expressed his sincere regret to those who have been hurt and affected by his activities and he repeats that apology most sincerely.
"He was effectively employed by News of the World from 2002 to carry out his role as a private investigator.
"As he accepted when he pleaded guilty in 2007 to charges of phone interception he admits that his role did include phone hacking.
"As an employee he acted on the instructions of others.
"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 has found himself facing questions over the extent of his involvement in the saga following fresh allegations that the former Sunday tabloid illegally accessed the voicemails of murdered schoolgirl Milly Dowler, relatives of victims of the 7/7 bombings in London, and grieving military families.
Today, MPs focused their attention on an email containing the transcripts of hacked voicemails and headed "For Neville", apparently a reference to the News of the World's former chief reporter Neville Thurlbeck.
James Murdoch told Mr Whittingdale's committee last week that he was unaware of the email and News Corp has always insisted that it learned the problem was not confined to a single "rogue" reporter only when papers were lodged in a civil court by the actress Sienna Miller late last year.
But following Mr Murdoch's testimony in front of MPs, the former News of the World editor Colin Myler and its legal manager Tom Crone said the head of News Corp in Europe and Asia was "mistaken".
They insisted they had informed him of the email when he signed off a reported £700,000 out-of-court settlement with Gordon Taylor, the chief executive of the Professional Footballers' Association, in 2008.
Today, Labour MP Tom Watson, who has led the phone-hacking campaign, said he had asked for Mr Murdoch to be recalled immediately but he had been voted down by his colleagues on the committee.
But Mr Whittingdale said there was "every chance" Mr Murdoch could be asked to re-appear but he wanted to take written evidence first.
He had written to Mr Myler and Mr Crone, asking them, and former News International director of legal affairs Jon Chapman to explain their statements following last week's select committee.
Mr Whittingdale told a press conference in Westminster: "Obviously we want to see the responses that they send to the letters that we are writing, but Tom Crone and Colin Myler and Jon Chapman have all said that they dispute the evidence given to this committee by James Murdoch.
"We want to hear exactly how they dispute that. I suspect it very likely that we will want to hear oral evidence. If they do come back with statements that are quite plainly different from those given by James Murdoch, we will want to hear James Murdoch's response to that.
"The chances are that this may well involve oral evidence from him as well."
Away from Westminster, the saga saw another high-profile departure as Baroness Buscombe, chairman of the Press Complaints Commission, said she would step down from her role following growing criticism of the watchdog.
The PCC said she would relinquish her post once a successor had been found but she would not continue beyond her three-year term of office, which comes to an end in the new year.
Announcing her decision, the 57-year-old stressed the need for the embattled PCC to continue its work but appeared to call for a tougher approach to media regulation.
In a statement, she said: "In this world of shifting media provision, I am convinced the answer to ethical concerns about the press is not statutory intervention.
"What is needed is a greater sense of accountability among editors and proprietors. A PCC with increased powers and reach remains the best way of achieving that."
It was also announced today that the Prime Minister David Cameron will face further questions about the scandal at 4pm on September 6 when he appears before the Commons Liaison Committee.
PA
