Image caption James and Rupert Murdoch initially declined an invitation to appear before MPs next Tuesday

News Corporation's Rupert and James Murdoch have agreed to appear before MPs to answer questions on the phone-hacking scandal on Tuesday.

The Commons media committee had issued summonses after the men initially declined to appear next week.

News International chief executive Rebekah Brooks had agreed to attend.

Meanwhile, Neil Wallis, ex-News of the World executive editor, was arrested on Thursday morning on suspicion of conspiring to intercept communications.

Mr Wallis, also a former member of the Editors' Code of Practice Committee, is the ninth person to have been arrested since the Metropolitan Police launched a fresh phone-hacking investigation in January.

The Murdoch-owned News of the World (NoW) was shut down last week amid the mounting scandal over the alleged hacking of phones belonging to crime victims, politicians and celebrities.

In the US, it is being reported that the FBI is investigating alleged hacking of the phones of 9/11 victims by the News of the World.

A growing group of senators and a senior Republican congressman have been calling for the authorities to investigate the allegations.

Democratic Senator Robert Menendez, who wrote to the attorney general to urge an investigation, said the claims newspapers sought to "exploit information about... personal tragedies for profit" needed to be probed.

I hope that in amongst the theatre that actually we do start to get some answers Martin Moore, Director, Media Standards Trust

'Serious questions'

On Tuesday, the UK's Commons culture, media and sport committee had invited the Murdochs and Mrs Brooks to give evidence at the House of Commons about the phone-hacking scandal.

In a statement, the MPs said that serious questions had arisen about the evidence Mrs Brooks and Andy Coulson, both of them former News of the World editors, gave at a previous hearing in 2003.

In his initial response to committee chairman John Whittingdale, Rupert Murdoch said that although he was not available on Tuesday, he was "fully prepared" to give evidence to the judge-led inquiry announced by the government.

James Murdoch offered to appear on an alternative date, the earliest of which was 10 August, while Mrs Brooks said she "welcomed the opportunity" to give evidence.

But after the committee issued summonses on Thursday morning for the men to appear, a few hours later News Corporation announced that the pair would attend the committee meeting.

In a letter to Mr Whittingdale confirming their attendance, James Murdoch wrote: "I hope that it is clear that we are committed to ensuring that the issues that have affected the News of the World are fully investigated and dealt with appropriately and robustly."

But he went on to warn the committee against encroaching on the public inquiry and police investigation of the phone-hacking allegations.

"We have been advised that, in the light of the fact that there are to be multiple reviews of the issues, this does carry the risk of prejudicing other judicial proceedings and in particular the ongoing police investigation and any potential subsequent prosecutions," he wrote.

"I would therefore respectfully ask you to take the utmost care in ensuring that the committee hearing does not run any risk of prejudicing that investigation and subsequent prosecutions."

The summonses were the first to be issued by a parliamentary select committee for almost 20 years, since the sons of the late newspaper tycoon Robert Maxwell were ordered to appear in 1992.

Committee chairman John Whittingdale said: "It will be the first time that Rupert Murdoch and James Murdoch, and indeed, Rebekah Brooks will have answered questions about this.

Media playback is unsupported on your device Media caption John Whittingdale: "There will be a whole range of questions people will want asking"

"They will be appearing before a parliamentary committee so I would hope they would take it seriously and they will give us the answers that not just we want to hear but I think an awful lot of people will want to hear," he told Sky News.

Martin Moore, director of the Media Standards Trust charity which campaigned for a public inquiry into phone-hacking, said the Murdochs' appearance before MPs would be "remarkable theatre".

"But I hope that in amongst the theatre that actually we do start to get some answers to the questions that most people will be asking," he said.

Menezes cousin

London mayor Boris Johnson is meeting Met Police Commissioner, Sir Paul Stephenson, to discuss the hiring of Neil Wallis as a consultant for the force, for which the journalist was paid £24,000.

Image caption Neil Wallis, a former executive editor of the News of the World, was arrested at 0630 BST on Thursday

It is understood that Home Secretary Theresa May has written to Sir Paul to get the "full picture" on the circumstances surrounding his appointment.

And the Home Affairs Select Committee has also written to ask him to give further evidence on the matter next Tuesday.

As part of the contract, Mr Wallis advised the Commissioner's Office, and the Directorate of Public Affairs and Specialist Operations, working closely with Assistant Commissioner John Yates.

Police are contacting about 30 suspected phone-hacking victims a week, the BBC understands, after investigations identified some 4,000 possible targets of the tactic.

The family of Jean Charles de Menezes, who was shot dead by police in July 2005, says the details of the mobile phone of his cousin were found in documents seized by police.

In other developments:

The government has published the advice given to Gordon Brown over launching an inquiry into News International, after the ex-prime minister claimed officials talked him out of taking action. Mr Brown said Cabinet Secretary Sir Gus O'Donnell warned him not to start a probe in 2010, as it was too close to a general election

Business Secretary Vince Cable told the BBC Radio 4 PM programme: "It is a little bit like the end of a dictatorship when everybody suddenly discovers they were against the dictator". He was stripped of his powers on media regulation after he told undercover reporters he had "declared war" on Rupert Murdoch in December 2010.

Chief Constable of Surrey Police Mark Rowley has told BBC Surrey he is "immensely frustrated" that, because of the Metropolitan Police investigation, he is not able to respond to claims his force was aware that murdered 13-year-old Milly Dowler's phone had been hacked

On Wednesday, Rupert Murdoch's News Corporation, whose UK arm - News International - owns the Sun, the Times, the Sunday Times and the now closed News of the World, dropped a bid to take complete control of satellite broadcaster BSkyB.