LONDON - Prime Minister David Cameron emphatically denied claims that his staff tried to stop an inquiry into phone hacking at the News of the World and defended his decision to hire one of the tabloid's editors as his communications chief.

In a raucous emergency session Wednesday in Parliament, Cameron did admit that both the ruling Conservatives and the opposition Labour parties had failed to pursue key developments in the hacking case and had actively courted media baron Rupert Murdoch.

"The clock has stopped on my watch and we need to sort it out," Cameron told lawmakers, promising that a government inquiry would examine the cozy relationship between British politicians and media and investigate whether other news organizations may have broken the law.

Police are also probing whether news media breached privacy laws.

Cameron cut short his Africa trip and the House of Commons delayed its summer break to debate issues engulfing both Britain's political and media elite and Murdoch's global communications empire, News Corp.

Murdoch owned the troubled News of the World, where the phone hacking claims first emerged in 2005, when the royal household alerted police that the tabloid may have learned about Prince William's knee injury by illegally intercepting phone messages.

Cameron's former communications chief Andy Coulson -- a former editor at the tabloid -- is among 10 people who have been arrested in the scandal. One has been cleared.

Lawmakers wanted to know why Cameron insisted on hiring Coulson despite warnings and how much the prime minister knew about the phone hacking investigation. There have been allegations that some people on Cameron's staff may have met with police to pressure them to drop the investigation.

"To risk any perception that No 10 (Downing Street) was seeking to influence a sensitive police investigation in any way would have been completely wrong," he said.

Cameron did, however, meet with News Corp. executives more than two dozen times from May 2010 to this month -- meetings that were criticized in Parliament by Labour leader Ed Miliband, who said Cameron had made a "catastrophic error of judgment" in hiring Coulson.

Coulson was an editor at the News of the World when royal reporter Clive Goodman and private investigator Glenn Mulcaire were arrested and jailed in 2007 for phone hacking. The original police inquiry into phone hacking was dropped, Coulson quit the paper and Cameron -- then opposition leader -- hired him.

This January, police reopened the hacking investigation. They are now investigating some 3,870 people whose names and telephone numbers were found in the News of the World files. It remains unclear how many were hacking victims. Coulson resigned his government post that same month.

News Corp. said Wednesday it had now eliminated legal payments to Mulcaire -- a day after Murdoch told lawmakers in a special parliamentary committee hearing that he would try to find a way to stop the payments. Mulcaire's lawyer, Sarah Webb, declined to comment on the development.

In other phone hacking news, a judge Wednesday awarded "Notting Hill" actor Hugh Grant -- one of the most prominent celebrity critics of the Murdoch empire -- the right to see whether he was one of the tabloid hacking victims.

The scandal captivated television audiences from America to Murdoch's native Australia on Tuesday, as Murdoch endured a three-hour grilling by U.K. lawmakers. The media baron said he had known nothing of allegations that staff at News of the World hacked into cellphones and bribed police to get information on celebrities, politicians and crime victims.

He also said he had been humbled by the allegations and apologized for the "horrible invasions" of privacy.

Murdoch flew out of London on Wednesday.

Politicians from both the Conservative Party and Labour Party have been tainted by the scandal.

During Wednesday's session, Miliband reminded Cameron that his own Deputy Prime Minister Nick Clegg had warned Cameron against bringing Coulson into Downing Street last year as communications chief. Clegg sat stone-faced during much of Wednesday's rowdy session.

Cameron later countered, saying the Labour Party was also guilty of hiring questionable characters, including Miliband's current strategist, Tom Baldwin, another former Murdoch journalist from a different paper.

Conservative donor Lord Ashcroft, a Belize-based billionaire who has funded the party for more than a decade, has accused Baldwin of trying to get private banking information in 1999.

Cameron defended Coulson's work and said if it emerged that Coulson had lied to him about his role in the hacking case he would take it seriously.

"Andy Coulson is innocent until proven guilty," Cameron said.

Buckingham Palace reacted sharply to a claim by one lawmaker that it had raised concerns with Cameron's office over his decision to hire Coulson. "It is outrageous to suggest this," said a palace spokesman.

Britain's Conservative Party reported it had just learned that another recently arrested phone-hacking suspect, former News of the World executive editor Neil Wallis, may have advised Coulson before the 2010 national election that put Cameron into power. It said Wallis was not paid for the advice, however.

Cameron also said the hacking affair raises questions over the ethics and values of London's police force and vowed Wednesday that he would bring in new leadership to the force. Two top police resigned this week over their close ties to Wallis.

Meanwhile, a House of Commons committee on Wednesday blasted both News International, the News Corp. unit that operates the British papers, and the London Metropolitan Police for their performance on the scandal.

"We deplore the response of News International to the original investigation into hacking. It is almost impossible to escape the conclusion ... that they were deliberately trying to thwart a criminal investigation," said the Home Affairs committee, which has been grilling past and present Metropolitan Police officials about their decision not to reopen the hacking investigation in 2009.

On Wednesday, police charged Jonathan May-Bowles, 26, with behaviour causing harassment, alarm or distress in a public place for trying to hit Murdoch with a foam pie at the U.K. hearing.

As the scandal exploded this month, Murdoch shut down the 168-year-old News of the World, gave up on buying full control of British Sky Broadcasting, Britain's biggest commercial television company, and accepted the resignations of two top executives.