David Cameron defended his handling on Monday of a corruption scandal around Rupert Murdoch's media empire which has swept away Britain's top police chief and raised questions about the prime minister's own future.

At a news conference in Pretoria, where he began what will be a curtailed visit to Africa, Cameron defended hiring former tabloid editor Andy Coulson, a figure at the centre of the scandal, as his spokesman.

He rejected veiled criticism from the police chief, who quit after coming under fire for appointing Coulson's former deputy as a media adviser to his force.

"The situation in the Metropolitan Police Service is really quite different to the situation in government," Cameron said in response to remarks by outgoing Metropolitan Police Commissioner Paul Stephenson, who contrasted the prime minister's response to hiring one ex-journalist to his own resignation over the other.

Having cut short a planned week in Africa as the scandal snowballed, Cameron also said parliament would delay its summer recess to let him address lawmakers again on Wednesday.

The prime minister came under further pressure on Sunday with the resignation of Stephenson and arrest of Rebekah Brooks, who ran British newspapers for Murdoch's News Corp.

Murdoch, the 80-year-old Australian-born magnate whose grip on Britain's media and politicians of all parties have been shaken by two weeks of outrage, faces a parliamentary committee on Tuesday. He and his son James, 38, as well as Brooks, can expect a fierce grilling over allegations the News of the World tabloid hacked thousands of people's voicemails and bribed policemen.

The scandal may be reshaping the British establishment, with the press, police and politicians all facing harsh questioning from the public over cosy relationships and a failure over many years to protect the vulnerable, including child crime victims and the nation's war dead, from intrusive tabloid journalism.

The affair has prompted Murdoch to shut down the 168-year-old News of the World, Britain's top-selling Sunday paper, and to drop a bid for pay-TV network BSkyB that was a key part of its global expansion in television. That in turn has raised questions from investors over the family's management.

News Corp shares plunged during Australian trading on Monday, hitting a two-year low of A$13.65 following global drama for the group during the weekend closure. On Friday, Brooks, a former News of the World editor, resigned, as did Les Hinton, head of Murdoch's Dow Jones & Co, publisher of the Wall Street Journal. Hinton used to run News International in Britain.

In resigning on Sunday, police chief Stephenson said he had done nothing wrong but did not want distractions from the affair to hamper security preparations for next year's London Olympics. And he aimed unusually sharp, if veiled, barbs at Cameron.

Amid public anger at the police's refusal for several years to act on allegations of widespread phone hacking, Stephenson had faced questions over his senior officers' closeness to News International. He was particularly under fire over the appointment of Neil Wallis, a former deputy editor at the News of the World, as a public relations adviser to his force.

Stephenson noted that Wallis, who was arrested last week and is one of 10 journalists so far being questioned as suspects in the phone hacking and bribery case, had not been linked to the scandal when he was hired. He contrasted that to Cameron's hiring in 2007 of Coulson, Wallis's editor at the paper.

Coulson resigned as editor when his royalty correspondent was jailed for hacking the phones of royal aides, although he denied knowing of any wrongdoing. Coulson quit the prime minister's office in January this year as police reopened their investigation of the paper. He was arrested this month. - Reuters