The News of the World (NoW) hired an ex-police officer early last year to carry out surveillance on two prominent lawyers representing victims of phone hacking, BBC Newsnight has learned.
Derek Webb covertly followed lawyers Mark Lewis and Charlotte Harris.
Mr Webb also filmed members of Mr Lewis's family - including his teenage daughter - on a shopping trip, which Mr Lewis said was "nothing short of sick".
News International, owners of the NoW, said it was "deeply inappropriate".
The surveillance of the lawyers, who have been involved in cases against NoW owner News International, took place during the past 18 months when James Murdoch was executive chairman.
Mr Murdoch is due to give a second round of evidence to a Commons select committee on Thursday.
The surveillance was part of an attempt by the now-closed tabloid newspaper to demonstrate that Mr Lewis was having a relationship with Ms Harris and was sharing confidential information with her.
Newsnight's Richard Watson said the aim was to gather evidence that confidential information was being leaked out - which would have been wrong - and a complaint could then have been made to the Solicitors Regulation Authority.
It is not clear who authorised the surveillance but Newsnight has seen evidence that its use was discussed.
The Metropolitan Police gave Mr Lewis documents, including emails from March 2010, which indicate a partner at News Group's lawyers, Farrer & Co, raised the idea of surveillance.
But there is no evidence surveillance was commissioned by Farrer & Co as a result and the firm told Newsnight it could not comment without permission from its employers, which it did not have.
Mr Lewis told Newsnight that he was "devastated" to hear the revelations.
"To follow my teenage daughter, my youngest daughter and video her is nothing short of sick," Mr Lewis said, urging that the matter be investigated.
"On another level looking at me, that's not how you litigate, you play the ball you don't play the man… this is Mafia-like."
Attempt to discredit
Mr Webb, who ran a private investigations firm called Silent Shadow, said he had been commissioned by the NoW to carry out surveillance on Mr Lewis and his former assistant Ms Harris in early 2010.
He was paid to go to Manchester, where the two solicitors were based.
On one occasion during the surveillance, Mr Webb followed Mr Lewis's former wife and his daughter, filming them as they visited shops and a garden centre before trailing them in a car as they returned home.
At the time Mr Lewis was proving a serious threat to the NoW by taking civil proceedings on behalf of phone hacking victims.
He had successfully won a payout of more than £500,000 for one of his clients, the chairman of the Professional Footballers' Association Gordon Taylor.
Other sources have told the BBC that advisers to the NoW were interested in the information as part of an attempt to discredit Mr Lewis and stop him from taking on other phone-hacking cases.
Investigator Derek Webb told Newsnight the NoW owed him compensation for his loyalty to the tabloid following eight years of service, but that he had not received any.
Mr Webb's background was in police surveillance and he was trained by the police and once attended an MI5 training course.
The paper folded in July after a string of hacking allegations emerged, including the phone of murdered schoolgirl Milly Dowler.
Mr Lewis represented her family, whose case led to the paper's closure.
Ms Harris represents football agent Sky Andrew and has represented actress Leslie Ash and her husband, former footballer Lee Chapman.
Mr Andrew is one of almost 50 alleged victims of media malpractice who have been granted the right to be "core participants" in the judicial inquiry into phone hacking, due to start on 14 November.
A News International spokesperson said: "News International's enquiries have led the company to believe that Mark Lewis and Charlotte Harris were subject to surveillance.
"While surveillance is not illegal, it was clearly deeply inappropriate in these circumstances. This action was not condoned by any current executive at the company."
Newsnight has also seen documents referring to the prime minister's former spokesman, Andy Coulson, who resigned from the News of the World after a reporter was jailed over phone hacking while he was the paper's editor.
They show News International was very sensitive about damaging his work with David Cameron around the time of the election.
At a meeting held to discuss phone hacking six days after the election, News Group's lawyer at Farrers stated he had been instructed not to do anything for three or four weeks to prevent further leaks around the election, because of "inevitable attacks" on Mr Coulson.
Tom Watson, a Labour MP who sits on the Commons' culture select committee investigating phone hacking, said it was another development which would shock people.
He said: "I think it shows an utterly relentless and ruthless organisation, clearly highly politicised and who would stop at nothing to try and cover this case up."
Richard Watson's full report on these allegation appeared on Newsnight on 7 November and is available on the BBC iPlayer and Newsnight website.