LONDON - Rupert Murdoch's Sky News channel twice authorized its reporters to hack into computers, a potentially embarrassing revelation that could further dent the media tycoon's hope of acquiring full control over satellite broadcaster BSkyB.

Sky News said in a statement Thursday that in one case it broke into emails belonging to Anne and John Darwin, the so-called "canoe couple" who became notorious in Britain after the latter faked his own death in a boating accident as part of an elaborate insurance scam. The circumstances surrounding the second case weren't made clear.

Sky News acknowledged intercepting the canoe couple's emails, but said the material was later handed to police and insisted it had done nothing wrong.

"We stand by these actions as editorially justified and in the public interest. We do not take such decisions lightly or frequently," Sky News chief John Ryley said in a statement.

He noted that, in a 2004 investigation, a Sky News journalists had bought an Uzi submachine gun to illustrate the availability of banned weapons in Britain. In 2003, a reporter sneaked into a restricted area at London's Heathrow Airport to highlight security failings.

"These investigations serve the public interest and are a legitimate part of responsible journalism," Ryley said.

Shares in BSkyB fell about 2.8 per cent following the news to 639 pence ($10.11).

A media frenzy was kicked off when John Darwin -- long thought to have died in a boating accident in the North Sea -- walked into a London police station in late 2007 and said: "I think I'm a missing person."

He claimed to have amnesia and said he could remember nothing since 2000, but his story unraveled as journalists and police started digging into his background.

Sky News didn't identify which of its stories was the result of hacking, but in an article dated July 21, 2008, journalist Gerard Tubb said the channel had uncovered documentary evidence showing that John Darwin had decided to come back to England because he was having trouble staying in Panama.

"We discovered an email," the article begins, without giving any explanation of how the message was obtained. Sky declined to make Tubb or Ryley available for interviews.

The company's public interest defence immediately drew skepticism from British legal experts.

David Allen Green, media lawyer at Preiskel & Co., said that there was no such thing as a public interest defence as far as Britain's Computer Misuse Act was concerned.

"It is not possible for the editor of any news organization to authorize criminal acts," said Green, who's been a frequent critic Murdoch's News Corp.

Britain's Crown Prosecution Service can decide, however, that it wouldn't serve the public interest to file charges.

"As Sky News took the hacked emails to the police themselves, it appears that any prosecution was decided not to be in public interest," Green said in a message posted to Twitter.

Sky's email hacking, first reported in Britain's Guardian newspaper, could be a further headache for Murdoch. His international media empire has spent the better part of a year in the spotlight over widespread illegal behaviour at his now-defunct News of the World tabloid, where journalists routinely hacked into public figures' phones in an effort to win scoops.

News Corp. owns a 39.1 per cent stake in BSkyB, which owns Sky News, and Murdoch was forced to abandon a potentially lucrative bid for full control of the broadcaster after the phone hacking scandal boiled over in July.

The scandal has increasingly embroiled BSkyB and Murdoch's son James -- the broadcaster's chairman until earlier this week.

James, the former head of his father's British newspaper division, has long insisted that he knew nothing of the widespread wrongdoing at the News of the World. With that claim coming under increasing scrutiny, the 39-year-old stepped down Tuesday in a move to insulate BSkyB from the scandal.

Opposition lawmaker Chris Bryant, whose own phone was hacked by the News of the World, said he was writing to BSkyB to ask when the company's board members knew about the hacking.

"Is this why James left?" Bryant asked on Twitter.

In a separate development, a person close to the case said that News of the World publisher News International was challenging celebrity phone hacking victim Sienna Miller over the size of her legal bill.

Miller won 100,000 pounds (about $160,000) from News International last year after the company admitted eavesdropping on her phone messages, but there's been no agreement on legal costs and the issue is headed to court, the person said. He spoke anonymously because the information wasn't cleared for release.

News International spokeswoman Daisy Dunlop declined comment, as did Miller's lawyer, Mark Thomson.

The phone hacking scandal has already cost News Corp. nearly $200 million, much of it in legal and consulting fees.