“There has been a catalog of failures by the Metropolitan Police, and deliberate attempts by News International to thwart the various investigations,” the home affairs committee chairman, Keith Vaz, said.

He was referring to new attempts by both the police and a separate inquiry, set up by Mr. Cameron, to be led by a judge investigating what happened.

“The new inquiry requires additional resources and if these are not forthcoming, it will take years to inform all the potential victims,” he said.

The questioning of the Murdochs was suspended briefly on Tuesday after a man attacked Rupert Murdoch with a foil plate of shaving cream. The police said the man, identified as Jonathan May-Bowles, 26, from Windsor, west of London, was charged on Wednesday with “causing harassment, alarm or distress in a public place” under the Public Order Act.

He was released on bail and ordered to appear in court again on July 29.

While the hacking scandal has been simmering for years, it exploded into a full-blown scandal earlier this month with reports that the voice mail of 13-year-old abducted girl, Milly Dowler, had been hacked on the orders of The News of the World in 2002 when Ms. Brooks was its editor.

The News Corporation on Wednesday said that it had stopped paying legal fees for Glenn Mulcaire, a private investigator for The News of the World who pleaded guilty to phone hacking charges and went to jail in January 2007, news agencies reported. Both Mr. Murdoch and his son James told members of Parliament on Tuesday that they were surprised to learn that the company had been paying his legal fees, as well as those of Clive Goodman, the tabloid’s royal reporter, who has also pleaded guilty to phone hacking. Wednesday’s announcement did not mention Mr. Goodman.

The scandal has spread to encompass Mr. Cameron’s decision to hire another former editor of The News of the World, Andy Coulson, as his media director both before and after the elections that brought him to power at the head of a coalition government in May 2010.