British Prime Minister David Cameron made a public admission of regret on Wednesday over the phone-hacking crisis, saying with hindsight he would not have hired ex-News of the World editor Andy Coulson.

To jeers from the opposition in the British parliament, Cameron defended his original decision to employ Coulson, who quit Downing Street in January and was arrested this month over the scandal at the paper, since shut by Rupert Murdoch.

But a day after cutting short a trip to Africa to confront the crisis, the under-pressure Conservative leader conceded he would not have employed Coulson had he been able to predict the furore of the past weeks.

"With 20-20 hindsight and all that has followed, I would not have offered him the job and I expect that he wouldnt have taken it," Cameron told lawmakers in the emergency session of the House of Commmons.

"You live and you learn and believe you me, I have learned."

Cameron refused to cut Coulson loose, however, telling lawmakers: "I have an old-fashioned view about innocent until proven guilty but if it turns out I have been lied to that would be a moment for a profound apology."

Opposition Labour party leader Ed Miliband demanded a full apology from Cameron, accusing him of ignoring repeated reports and warnings over Coulson.

"It was a deliberate attempt to hide from the facts about Mr Coulson," Miliband said.

A day after Rupert Murdoch faced a grilling from British lawmakers over the scandal that closed his News of the World paper earlier this month, it was Cameron's turn to take the heat over the controversy.

He has come under intense pressure over his decision to hire Coulson, shortly after the journalist quit as editor of the News of the World in 2007 following the jailing of two peole at the tabloid over phone hacking.

Coulson has always denied wrongdoing but he was arrested earlier this month over the scandal and allegations of police bribery.

Cameron on Wednesday admitted that another arrested former executive from the paper, Neil Wallis, may have advised Coulson before last year's general election but said his Conservative party had not paid him.

The scandal has torn through Australian-born Murdoch's News Corp. empire, which owned the News of the World, leading to the resignation of two of his top aides, Rebekah Brooks - a friend of Cameron - and Les Hinton.

Hours before Cameron's statement to parliament, lawmakers released a report which was highly critical of attempts by Murdoch's News International, his British newspaper wing, to 'thwart' the phone-hacking investigations.

"There has been a catalogue of failures by the (London) Metropolitan Police, and deliberate attempts by News International to thwart the various investigations," said lawmaker Keith Vaz, chairman of the Home Affairs Select Committee.

The report strongly criticised senior police officer Andy Hayman, who led the original probe in 2006, saying his conduct was 'both unprofessional and inappropriate'.

It criticised him for taking a job with the Murdoch-owned Times newspaper shortly after leaving the police.

"We deplore the fact that Mr Hayman took a job with News International within two months of his resignation and less than two years after he was - purportedly - responsible for an investigation into employees of that company," it said.

The original police hacking probe led to the jailing of the News of the World's royal editor and a private investigator.

But despite mounting evidence that the practice was more widespread, the evidence lay untouched for years until police finally revived the probe in January.

New claims that an investigator working for the paper hacked into the phones of murdered teenager Milly Dowler and the relatives of dead British servicemen turned the controversy into a national outrage.

When a parliamentary committee grilled Murdoch and his son James on Tuesday, he said it was 'the most humble day of my life' but denied that he had ultimate responsibility for the scandal.

His testimony was interrupted when a protester splattered a foam pie over the 80-year-old. Murdoch's Chinese-born wife Wendi Deng sprang to his defence.

Police early on Wednesday charged Jonathan May-Bowles, 26, over the attack.