LONDON — An apologetic Prime Minister David Cameron distanced himself Wednesday from his former communications director, telling an emergency session of Parliament he never would have hired the ex-tabloid editor if he had known about the newspaper's phone-hacking scandal.
"Of course I regret, and I am extremely sorry, about the furor it has caused," Mr. Cameron said of hiring Andy Coulson, who resigned in January just as the News of the World's scandal was getting widespread attention.
Mr. Cameron, the Conservative Party leader, has weathered fierce criticism from opposition lawmakers about his links to Mr. Coulson, the tabloid and its owner, media baron Rupert Murdoch.
The prime minister's tense session convened a day after Mr. Murdoch, his son James and his former lieutenant, Rebekah Brooks, testified before a parliamentary panel about the scandal. All have pleaded ignorance of phone-hacking allegations.
The political stakes are high: The now-defunct News of the World is accused of illegally intercepting cellphone messages of thousands of people and paying police for information, and public opinion is almost entirely negative.
What's more, the scandal is forcing a growing number of resignations:
• Ms. Brooks, who was the tabloid's editor when the hacking is alleged to have occurred, last week quit her post in Rupert Murdoch's global media empire, News Corp.
• Also last week, Les Hinton quit as head of Dow Jones, publisher of the Wall Street Journal — one of the Murdochs' U.S. firms.
• This week, London police Chief Paul Stephenson and assistant police Commissioner John Yates resigned over their force's ties to a former tabloid editor and a decision not to probe the scandal years ago.
At least 10 people, including Mr. Coulson and Ms. Brooks, have been arrested in the police's phone-hacking probe, one of two investigations into the matter. And five police officials, including Mr. Stephenson and Mr. Yates, are being investigated for their roles in the scandal.
The opposition has sensed a moment of opportunity and is applying pressure on the ruling Conservatives, even though Rupert Murdoch has long associations with key members of both political parties.
Labor Party leader Ed Miliband said Wednesday the prime minister had built a "wall of silence" around Mr. Coulson's employment and ignored five warnings about his alleged involvement in the phone hacking before being appointed as Mr. Cameron's spokesman.
"This cannot be put down to gross incompetence," Mr. Milliband said. "It was a deliberate attempt to hide from the facts about Mr. Coulson."
Political and media analysts have said they expect more resignations among the press corps and the police department but not in the political realm, prompting legislators to question politicians' apparent impunity.
"A lot of people will be asking, 'Is there one set of rules for metropolitan police and another for politicians?' " Labor lawmaker Chris Bryant, who accuses the tabloid of illegally accessing his phone, told the BBC.
Conservative lawmaker Nicky Morgan dismissed suggestions that Mr. Cameron should step down and said the government had moved to investigate phone hacking with all due speed.
"I think that's what the Labor Party would love and clearly they're pushing for it," Ms. Morgan said. "When you're in government, it's very different from being in opposition. It took time to put in place a sufficiently robust inquiry mechanism."
Mick Hume, a former Times of London columnist, said the growing political crisis is borne of weakness, rather than the actual significance of the scandal itself.
"It does show the weakness of the right, or what we used to call the right," he said. "They're chasing to catch up with the illiberal liberals. Whether that translates into votes [at the next election] is another matter. Labor is finding its sense of mission in outrage [rather than policy]."
Mr. Miliband has dismissed calls for statutory regulation of the press but has called for reform. Taking a clear swipe at News Corp., he said his party will submit proposals for new regulations on cross-media ownership.
"The [scandal] has exposed an unhealthy situation involving both of the main political parties, Labor before and the Conservatives afterwards, in the way politicians have courted favor with News International," said media law consultant David Banks.
"The news organizations are there to hold politicians to account and expose what they are doing. They are not supposed to be in cahoots."
• Ms. Osborne reported from London, and Mr. Walsh from Belfast.