LONDON — The cozy relationship that Rupert Murdoch long enjoyed with the British power structure came to an abrupt end Tuesday, just as he needed it to complete one of his biggest media buys ever.

The billionaire, tainted by a cell phone hacking scandal at one of his newspapers, suddenly faces stiff government opposition to his bid for total control of a much more lucrative property: the satellite British Sky Broadcasting company.

The news came in a stunning announcement from Prime Minister David Cameron’s office that the government will support a motion calling on Murdoch and his News Corp. to withdraw the $12 billion bid for BSkyB.

Cameron’s turnabout means the Australian-born Murdoch, who held great influence in British politics no matter who ran the government, suddenly finds all three major political parties lined up against him. He’s even been asked to appear before lawmakers next week to answer questions about the conduct of News International, Murdoch’s UK company.

A resolution calling for the scrapping of the BSkyB deal would be nonbinding but would likely be seen as a powerful expression of united opposition to any substantial expansion of Murdoch’s holdings. The deal is awaiting regulatory approval.

The long-brewing hacking scandal at Murdoch’s News of the World tabloid turned into a crisis for the media magnate this month following allegations that the paper’s employees hacked the phone of Milly Dowler, a 13-year-old murder victim, and deleted several messages in 2002.

In response, News International closed the tabloid for good Sunday, but that has not stemmed the outrage among Britons or stopped new hacking allegations from emerging.

Cameron, who has enjoyed friendships with some top Murdoch executives, took action after his predecessor, Gordon Brown, gave an emotional televised interview Tuesday saying that Murdoch journalists with ties to the criminal underworld invaded his family’s privacy as well.

Brown said Murdoch’s papers, including the Sun and the Sunday Times, had used fraudulent and criminal means to obtain his confidential bank accounts, tax records and even health information about his son, who suffers from cystic fibrosis.

He said he was in tears after learning The Sun planned to publish stories about his son’s illness, which had been kept within the family. But he told the BBC that it was people “at rock bottom” who were most brutally exploited.

“What about the person, like the family of Milly Dowler, who are in the most desperate of circumstances, the most difficult occasions in their lives, in huge grief and then they find that they are totally defenseless in this moment of greatest grief from people who are employing these ruthless tactics with links to known criminals?” Brown said.