Ofcom has opened an investigation into Rupert Murdoch's Sky News channel after the channel admitted it had hacked into someone's private email account in pursuit of a story.

Britain's broadcasting regulator said in a statement that it has started probing the circumstances around the hacking, which Sky News has maintained was in the public interest.

"Ofcom is investigating the fairness and privacy issues raised by Sky News' statement that it had accessed without prior authorisation private email accounts during the course of its news investigations," said an Ofcom spokesman.

"We will make the outcome known in due course."

The regulator is expected to have completed its investigation within 90 working days.

Sky's head of news John Ryley admitted on 5 April that the broadcaster's journalists hacked the email accounts of John Darwin, the "canoe man", and his wife Anne Darwin.

Mr Darwin faked his own death in after paddling in his canoe off the coast of Hartlepool.

He went missing and was thought to be dead having been lost at sea in his canoe, allowing his wife to claim on his life insurance policy.

After several years he walked into a police station pretending to have amnesia, but both he and his wife were convicted of fraud and handed jail terms in 2009.

Sky News hacked the pair's emails and helped uncover the fraud.

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

"They require finely balanced judgement based on individual circumstances and must always be subjected to the proper editorial controls."

Ofcom's broadcasting code contains a rule, clause 8.1, that states: "Any infringement of privacy in programmes, or in connection with obtaining material included in programmes, must be warranted."

Despite the new Ofcom investigation, Sky maintained its stance.

"As the head of Sky News, John Ryley, said earlier this month, we stand by these actions as editorially justified," a spokeswoman for Sky News said.

"The Crown Prosecution Service acknowledges that there are rare occasions where it is justified for a journalist to commit an offence in the public interest.

"The Director of Public Prosecutions Kier Starmer told the Leveson inquiry that 'considerable public interest weight' is given to journalistic conduct which discloses that a criminal offence has been committed and/or concealed."

After the initial admission in early April, BSkyB, the Murdoch company under which Sky News operates, watched the value of its shares plunge 4 percent.

BSkyB stock has for the most part recovered since then.

Its price was up 1.04 percent on the day to 681.50 at 11:51am London time.