News International Chief Executive Rebekah Brooks has agreed to give evidence to MPs over the phone hacking scandal next week, it has been announced.
But the Commons Culture Select Committee has issued a summons to media mogul Rupert Murdoch and his son James after they said they were unavailable to attend the session. The younger Murdoch had offered to appear on August 10 instead.
It is not clear whether the committee will be able to compel the men to face questioning as they are US citizens.
In his letter to committee chairman John Whittingdale, Mr Murdoch senior said that although he was not available on Tuesday, he was "fully prepared" to give evidence to the judge-led inquiry announced by David Cameron.
"I will be taking steps to notify those conducting the inquiry of my willingness to do so," the letter said. "Having done this, I would be happy to discuss with you how best to give evidence to your committee."
The development came after Deputy Prime Minister Nick Clegg insisted Mr Murdoch should submit to a grilling by the committee if he has a "shred of responsibility".
Earlier on Thursday former News of the World executive editor Neil Wallis was arrested at his home in west London by detectives from Operation Weeting, the Scotland Yard investigation into mobile interceptions by the Sunday tabloid, said sources.
He became deputy editor of the News of the World in 2003 and served under Andy Coulson's editorship before becoming the paper's executive editor in 2007.
Mr Coulson, 43, who was Downing Street communications chief until January this year, was himself arrested by Operation Weeting officers on Friday over alleged phone hacking and illegal payments to police. He was released on bail until October.
Wallis is a former member of the editors' code of practice committee of the Press Complaints Commission, the British newspaper industry's self-regulating body that has been accused by politicians of being too weak to tackle serious journalistic malpractice. He is the ninth person arrested since the Metropolitan Police launched a fresh investigation into phone hacking in January.
Photo by pete riches, article by The Press Association