Analysts say Rupert Murdoch's grip on his global media empire could be slipping as the News Corp boss prepares for an interrogation by angry British MPs tonight and his share prices continue to fall.

News Corporation Class A shares trading on the New York stock exchange closed down more than 4 per cent, or 67 cents, to $14.96 this morning, and the Class B Voting shares were down by a similar amount.

Shares in the company fell another 4 per cent on the Australian share market yesterday, closing at a two-year low of $14.16.

Australian-listed News Corp shares bounced back 2.4 per cent to $14.50 by the close of trade, on reports that Rupert Murdoch may step aside from management.

However, a board director denied reports that a meeting had taken place to discuss the possibility of Mr Murdoch stepping aside.

"There was no meeting of independent directors. This board totally supports the top management. We're united behind him," the board member told Reuters.

News Corp shares remain down nearly 20 per cent since the saga began, with some analysts estimating the company's value has dropped by around $9 billion.

Almost $1 billion has been wiped from the value of the Murdoch family's News Corp shareholding alone since the phone hacking scandal began, according to data compiled by financial services firm Bloomberg.

Senior analyst at BBY Mark McDonnell has told ABC News Breakfast that if the stock continues to slide the 80-year-old Mr Murdoch may have no choice but to step aside.

"Precisely because he is such a substantial shareholder... if there is in fact a widely perceived discount to the share price associated with his continuing hold on to the executive chairmanship, then of course that may become something that he sees as easily resolved by stepping aside," he explained.

Mr Murdoch will be the centre of attention tonight (Australian time) when he joins his son James and former News International boss Rebekah Brooks in front of a British parliamentary inquiry.

The appearance comes after another top-ranking Scotland Yard officer was forced to stand down over his handling of the News of the World hacking scandal.

Assistant commissioner John Yates, who decided in 2009 not to reopen the investigation into the News of the World, had been facing calls for his resignation from the civilian body that oversees the force.

His resignation came less than a day after Britain's top policeman Sir Paul Stephenson stepped down and Ms Brooks was questioned by police as the scandal continued to rock the UK establishment.

Also overnight, former News of the World reporter and phone hacking whistleblower Sean Hoare was found dead at his home north of London. Police said the death was not suspicious.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 2 minutes 48 seconds 2 m 48 s Hacking scandal claims another top cop ( ABC News )

Executive independent directors at the company are already asking questions about Rupert Murdoch's leadership and Mr McDonnell says News Corp could run quite effectively without someone from the Murdoch family at the helm.

He says that if Rupert Murdoch is forced to step aside there are a lot of talented people in the company to replace him.

"Chase Carey is effectively the second-in-charge for the group internationally, David DeVoe is the chief financial officer, you've got major parts of News Corp run out of the United States, for example 20th Century Fox etc, etc," he observed.

"Its an organisation with great depths of management and executive talent."

There was a further blow to the company this morning, with ratings agency Standard & Poor's, which has been looking at News Corporation's BBB+ corporate debt, placing it on credit watch negative.

Standard and Poor's has cited the potential damage to News Corp's reputation and its business from the probes into phone hacking.

Porter Bibb, of Mediatech Partners in the United States, called an investment in News Corporation at the moment 'dead money'.

"This thing now really has exploded to the point where Rebekah Brooks has now been arrested. I would not be surprised if James [Murdoch] is not the next. Les Hinton, Les Hinton is certainly going to be charged as well, and the company is at risk right now," he said.

"News Corp is a very, very good, very strong, very profitable company, but it's in jeopardy, and 'The Street' has called investing in News Corp today 'dead money'."