London (CNN) -- UK news channel Sky News said Thursday it had authorized its journalists to hack illegally into the e-mail of individual members of the public on two occasions.
John Ryley, head of Sky News, said the instances involved suspected criminal activity.
"We stand by these actions as editorially justified and in the public interest," he said in a statement. "We do not take such decisions lightly or frequently."
An external review of e-mail records is under way at the broadcaster's instigation, he said, but no grounds for concern have yet been found.
"Sky News is committed to the highest editorial standards. Like other news organizations, we are acutely aware of the tensions that can arise between the law and responsible investigative journalism."
Ryley said a journalist had been authorized on two occasions to access the e-mail of individuals suspected of criminal activity.
One case was that of Anne Darwin, he said. The British woman's husband faked his death on a canoe trip in order to falsely claim life insurance payments. Sky News then passed the e-mails to the local police force, he said.
"Material provided by Sky News was used in the successful prosecution, and the police made clear after the trial that this information was pivotal to the case," Ryley said.
Writing on the Sky News blog Thursday, Ryley said the company's admission on hacking followed a story published by the Guardian newspaper examining Sky News's role in the 2008 conviction of Anne Darwin.
He questioned the newspaper's motivation for writing the story, saying it and other media organizations have previously admitted obtaining information in unlawful ways.
"Some of the most important stories have involved breaking the rules in some way," Ryley said.
The news comes only two days after James Murdoch -- the son of media magnate Rupert Murdoch -- stepped down as chairman of satellite broadcaster BSkyB, which owns Sky News, part of the News Corp. empire.
His resignation came amid accusations that News Corp.'s British Sunday tabloid the News of the World systematically eavesdropped illegally on crime victims, politicians, celebrities and veterans in search of stories.
Murdoch has consistently denied knowing about the scale of phone hacking at the paper, which he ordered shut down last summer in the face of the scandal.
He referred to it in his resignation statement, saying: "I am determined that the interests of BSkyB should not be undermined by matters outside the scope of this company."
He made clear he was trying to shield the satellite broadcaster from fallout from the newspaper scandal, saying: "I believe that my resignation will help to ensure that there is no false conflation with events at a separate organization."
Labour member of Parliament Tom Watson, who has been a prominent figure in the probe into alleged phone hacking, told CNN the latest Sky News revelation was "pretty extraordinary."
Watson said he wanted the new chairman of BSkyB, Nick Ferguson, to say whether the company thinks the practice was more widespread, when the board was informed and what safeguards will be put in place to stop it happening again.
In his statement Thursday, Ryley said Sky News had commissioned an internal audit of payment records, alongside the external review of e-mail records.
Any impropriety found would be swiftly investigated, he said. "We believe these proactive steps, undertaken at our own initiative, form part of the good governance procedures to be expected of a responsible news organization."
London's Metropolitan Police are conducting three investigations into alleged misconduct by journalists.
One involves potential computer hacking on behalf of newspapers, a second is focused on alleged voicemail hacking, and the third concerns allegations of police bribery.
The government also set up an independent inquiry to look into media misconduct, and parliament's media committee has held hearings with witnesses including James Murdoch and his father.
James Murdoch resigned as chairman of News International, the UK newspaper publishing arm of News Corp., in February. The company said he would focus instead on its pay television businesses and broader international operations.
News Corp. shelved its plan to expand its ownership of BSkyB last summer as the phone hacking scandal broke.
CNN's Dan Rivers and Bharati Naik contributed to this report.