It's going to be a long, hard day for one of world media's most powerful figures as he attempts to fight off a scandal that has crossed the Atlantic.

Rupert Murdoch's car was today mobbed by photographers as he arrived for a grilling from U.K. lawmakers about the phone hacking scandal that has swept from his media empire through the London police and even to the British Prime Minister's office.

Murdoch's Range Rover was surrounded as he arrived at the Houses of Parliament three hours early, and once inside, the magnitude of the scandal was obvious.

The tycoon told British MPs that he faced 'the most humble day of my life' as he and son James gave evidence over activities at the shuttered News of the World.

"This is the most humble day of my life," the 80-year-old Murdoch, the Australian-born head of the global News Corporation empire, said in a brief opening statement to the committee.

Murdoch, whose Chinese-born wife Wendi was also in the room, said it was 'not an excuse' but that with an empire of 53,000 staff to oversee he could not be held fully responsible for failing to uncover the scandal.

James, 38, the chairman of Murdoch's British newspaper operation News International, apologised to victims of the scandal, who include a teenage murder victim, families of dead soldiers and victims of terror attacks.

"I would like to say just how sorry I am and how sorry we are to particularly the victims of illegal voice mail interceptions and to their families," James Murdoch said.

Former News International chief executive Rebekah Brooks is due to testify later.

They appeared shortly after Cameron admitted the country had a 'big problem' and cut short a trip to Africa.

In a further tragic twist, British police were investigating the unexplained death of whistleblower Sean Hoare, a former reporter at the newspaper who first implicated Cameron's ex-spokesman Andy Coulson in the scandal.

"This is a big problem but we are a big country," Cameron said after meeting Nigerian President Goodluck Jonathan in Lagos, adding: "We are going to sort them out."

Cameron, who is due to fly home to address an emergency session of parliament on Wednesday, added that his government would not lose its focus on the key challenges facing Britain, including restoring growth after the recession.

Dozens of people queued up to get into the hearing of parliament's Culture, Media and Sport committee to hear the two Murdochs and Brooks, until recently the three most powerful people in the British media.

Lawmakers also heard evidence from outgoing Scotland Yard chief Paul Stephenson, who quit on Sunday amid questions over the force's links with Neil Wallis, deputy editor at the News of the World when Coulson edited the paper.

Stephenson admitted that 10 members of the Metropolitan Police press office had worked at News International.

But he denied taking a 'swipe' at Cameron in his resignation statement and comparing the force's employment of Wallis to Coulson.

Both Coulson, who left Downing Street in January, and Wallis have since been arrested and bailed on suspicion of phone hacking.

With New York-based News Corp. also facing a probe in the United States and shares plummeting, Murdoch, now a naturalised US citizen, reportedly engaged public relations consultants to train him for Tuesday's session.

James Murdoch, chief executive of News Corp's Europe and Asia operation, was set to face questions over payments he is alleged to have approved to the victims of hacking.

The flame-haired Brooks, also a former editor of the News of the World, was arrested on Sunday on suspicion of hacking and bribing police.

The Murdochs initially refused to appear before the committee but relented after they were formally summoned.

Ed Miliband, the leader of the opposition Labour Party, called on them all to issue a full public apology.

"What members of the public will want to know is whether Rupert and James Murdoch and indeed Rebekah Brooks have some remorse for what happened, and are willing to apologise and say they have let down the British people," he said.

News International was meanwhile targeted overnight by the Lulz Security hacker group, which replaced The Sun newspaper's online version with a fake story saying Australian-born Rupert was dead.

The initial police investigation into the Sunday tabloid resulted in the jailing of the paper's former royal editor and a private investigator but the evidence then sat untouched for years.

When the probe was eventually reopened in January, detectives found thousands more alleged hacking victims, including Milly Dowler, a murdered 13-year-old schoolgirl.

Meawnwhile, police said a post mortem was being carried out on Hoare, a former News of the World showbusiness reporter, who alleged in interviews with The New York Times newspaper and the BBC last year that Coulson knew about voicemail hacking.

Hoare was found dead early on Monday at his home in Watford, north of London, Hertfordshire Police said in a statement. "The death is currently being treated as unexplained, but not thought to be suspicious," it said.

The Guardian newspaper said Hoare had long-term drink and drug problems.