Prime Minister David Cameron will be grilled by parliament on Wednesday about his decision to employ a former tabloid newspaper editor caught up in a phone-hacking scandal that has rocked Britain's establishment.

Britain's Prime Minister David Cameron delivers a speech on growth and trade to delegates at the The Pan African University Business School in Lagos July 19, 2011. Cameron cut short a trip to Africa and will fly home on Tuesday to defend himself from a scandal that has battered Rupert Murdoch's media empire, forced British police chiefs to resign and raised doubts about the prime minister's judgment.[Agencies]

The scandal, centred on Rupert Murdoch's News Corp global media empire, has forced the resignations of senior executives at the company and two of Britain's top policemen as well as fuelling opposition attacks on Cameron's judgment.

The 80-year-old Murdoch was attacked by a protester with a foam pie when he appeared before a parliamentary committee on Tuesday and made a "humble" apology for the scandal but refused to resign. He said staff who "betrayed" him were at fault.

Analysts said Murdoch's televised apology had now put the spotlight on how Cameron emerges from scrutiny in the emergency parliamentary debate over the scandal, which has included allegations of hacking into a murdered schoolgirl's voicemail and the phones of British troops killed in combat.

A few hours before Cameron was due to face legislators at 1030 GMT, another cross-party parliamentary committee published a report criticising both News International, the British arm of News Corp, and the police over the phone-hacking investigation.

"There has been a catalogue of failures by the Metropolitan Police, and deliberate attempts by News International to thwart the various investigations," said Keith Vaz, the chair of the Home Affairs committee.

The scandal is unlikely to bring down Cameron, in office for less than 15 months, but could make it harder for him to manage a Conservative-led coalition that is focused on quick deficit reduction, which has labour unions threatening mass strikes.

Cameron cut short a trip to Africa for the debate, with the opposition Labour Party determined to put him on the rack over why he employed Andy Coulson, a former editor of Murdoch's News of the World tabloid, which was shut down over the scandal.

"The Murdochs can say they apologised unreservedly, they faced the music, (and) they endured a personal physical attack," said Andrew Hawkins of polling company Comres.

"It puts the attention firmly back on the political ramifications and, in particular, David Cameron and his judgment over the whole Andy Coulson issue," said Hawkins.

Labour leader Ed Miliband has already put pressure on Cameron over Coulson, who resigned as editor of the News of the World but denied any wrongdoing after two people employed by the newspaper were jailed for phone-hacking in 2007.

Then opposition leader Cameron appointed Coulson as his communications chief that year and kept him on becoming prime minister in May 2010. He has said he gave Coulson the job because there was no evidence of his involvement in hacking.

Coulson quit his government role in January days before police launched a new investigation, and Miliband turned up the heat on Cameron when the former editor was arrested for questioning earlier this month and then freed on bail.

Speaking in Nigeria before flying home, Cameron signalled a desire to push the agenda away from a scandal that has dominated every debate for two weeks.

"The British public want something else too," Cameron said.

"They don't want us to lose our focus on an economy that provides good jobs, on an immigration system that works for Britain, a welfare system that is fair for our people."