Rupert Murdoch's son-in-law says family members are "ashamed and sickened" of the mogul's right-wing channel Fox News, in what Murdochologists said could be the opening salvo in a public battle for the soul of America's most-watched news channel.

The attack on Fox by Matthew Freud, the British public relations guru who is married to Elisabeth Murdoch, caused an immediate sensation in the media industry, as much for the fact that it was made in public as for the strength of the words chosen.

And attention was focusing last night on the future of Fox's combative founder and boss, Roger Ailes, the former aide to Richard Nixon who shaped the channel's coverage in his own image as a right-wing rabble-rouser.

Fox emerged as a counterpoint to the perceived liberal bias of CNN and became the strongest cheerleader for the presidency of George W Bush, under its slogan of "fair and balanced" journalism. Since the election of Barack Obama, the channel has given voice to opponents of the President and was boycotted by the White House over the summer for inflaming protests against proposed healthcare reform.

Agreeing to contribute his thoughts to a New York Times profile of Mr Ailes, Mr Freud stated: "I am by no means alone within the family or the company in being ashamed and sickened by Roger Ailes's horrendous and sustained disregard of the journalistic standards that News Corporation, its founder and every other global media business aspires to."

Mr Ailes has long been rumoured to have a tempestuous personal relationship with Rupert Murdoch, while the mogul's children are known to have substantially more liberal views than those on show on Fox. A recent biography of Mr Murdoch, The Man Who Owns The News by Michael Wolff, described how the mogul's wife, Wendi Deng, persistently urged her husband to rein in the political coverage on Fox.

Mr Wolff said last night that Mr Freud's statement could only be interpreted as a calculated attempt to put pressure on Mr Ailes. "Matthew Freud, a PR man of extraordinary craftiness, is not going to say anything off the cuff, certainly not that. I have never heard a shoe drop as loud. I don't believe Roger Ailes can continue in this company. Not only has he been told that its controlling shareholders don't want him, but he has been told they think he is despicable. Something has just been set in motion."

Mr Murdoch turns 79 in March, and has long been grooming his children to succeed him in running News Corporation, the family-controlled media giant, where Fox News is increasingly seen as the most valuable journalistic asset. The company also owns The Times, The Sun and BSkyB in the UK, the Wall Street Journal, and Twentieth Century Fox movie studio, among other businesses.

The family's voting rights will eventually be shared amongst Mr Murdoch's adult children. Of the four, only James Murdoch now works for News Corp, overseeing all its European and Asian divisions. Elisabeth currently runs her own TV production business in the UK.

Mr Ailes was paid $23m in salary, bonuses and benefits last year, more than Rupert Murdoch himself. The two men are said to have clashed over Mr Murdoch's flirtation with the idea of endorsing Mr Obama for the presidency last year. In the end, the company's US tabloid, the New York Post, stayed Republican but Mr Murdoch gave political donations to both sides.