Rupert Murdoch defiantly insisted on Tuesday he was not responsible for what he called "sickening and horrible invasions" of privacy committed by his company, claiming he had been betrayed by disgraceful unidentified colleagues and had known nothing of the cover-up of phone hacking.

During a three-hour grilling at the culture select committee, disrupted by a protester throwing a plate of shaving foam, the once all-powerful News Corp chairman and chief executive told MPs: "I am not responsible."

In a halting performance, at times pausing, mumbling and mishearing, Murdoch said those culpable were "the people I hired and trusted, and perhaps then people who they hired and trusted". But he denied the accusation he had been "willfully blind" about the scandal.

Flanked by his son James, the chairman of News International, Murdoch said he and his company had been betrayed in a disgraceful way, but argued he was still the best person to clean up the company, adding in a rehearsed soundbite that his day in front of the committee represented "the most humble day of my life".

In a Westminster hearing screened worldwide, he repeatedly tried to avoid identifying the specific culprits in his company, often blaming earlier legal counsel for inadequate advice or leaving his son to explain his behaviour.

But in separate testimony to the home affairs select committee, Lord Macdonald, the former head of the CPS, revealed it had taken him three to five minutes to examine documents kept by the company's solicitors showing widespread criminality at the company.

Macdonald said in his view the criminality revealed was "completely unequivocal", adding when he reported his findings to the News Corporation board recently there was surprise and shock. He said: "I cannot imagine anyone looking at the file would not say there was criminality," including payments to police.

The file was kept at the solicitors Harbottle & Lewis, and the police investigation is now centring on which executives tried to conceal its contents. In May 2007 Harbottle & Lewis sent a two-paragraph letter to News International executives claiming their examination of the documents showed there was no evidence any senior executives knew of illegal activities by the reporter Clive Goodman, or of any other illegal activities.

The physical assault on Murdoch came near the end of the evidence session, prompting gasps as his wife, Wendi Deng, leaped up to hit the assailant, Jonathan May-Bowles, a participant in UK Uncut events.

May-Bowles was detained by police as James Murdoch angrily asked officers why they had not protected his father. The Commons Speaker, John Bercow, called for an inquiry.

The culture and home affairs select committees between them took more than eight hours of evidence about the phone-hacking scandal. Under cover of the drama of the hearings, the Conservatives revealed that Neil Wallis, a former News of the World deputy editor, had given "informal unpaid advice" to Andy Coulson when he was director of communications at the Conservative party.

In a statement the party said: "It has been drawn to our attention that he may have provided Andy Coulson with some informal advice on a voluntary basis before the election. We are currently finding out the exact nature of any advice."

Wallis was arrested last week on suspicion of phone hacking, and the furore surrounding his hiring by the Metropolitan police between October 2008 and September 2009 has led to the resignation of Sir Paul Stephenson, the Metropolitan police commissioner, and the Met's assistant commissioner John Yates, who both gave evidence on Tuesday.

Separately emails were released by Downing Street showing David Cameron's chief of staff, Ed Llewellyn, had on 20 September 2010 turned down the opportunity of a briefing by the Metropolitan police on the phone hacking. Labour claimed it showed an extraordinary dereliction of his duty to find out the scale of wrong-doing and the potential involvement of Coulson, the former No 10 director of communications.

Cameron will be pressed on the issue when he makes a statement to MPs on how he is handling the crisis. He has been summoned to a 1922 backbench committee meeting to justify his response, including his decision to hire Coulson.

The publication report from the all-party home affairs committee, which has been brought forward in time for Cameron's statement today, has found that News International "deliberately" tried to block a Scotland Yard criminal investigation into phone hacking at the News of the World. The report finds the company "deliberately" tried to "thwart" the 2005-6 Metropolitan police investigation into phone hacking carried out by the tabloid.

Much of the cross-examination of the Murdochs was largely designed to locate how high the apparent cover-up of systematic law-breaking went. James Murdoch was forced to admit, after much wriggling, that his company was still paying the legal costs of Glenn Mulcaire, one of the private detectives on the payroll of News of the World found guilty of hacking phones. James Murdoch said he was shocked and surprised to learn the payments were continuing, and denied it had been done to buy silence.

Pressed by the Labour MP Paul Farrelly, Rupert Murdoch said he would stop the payments if he was contractually free to do so. James Murdoch denied the large out-of-court settlements to the PFA chief executive, Gordon Taylor (£700,000), and publicist Max Clifford (£1m including legal costs), authorised by him in 2008, had not been pitched so high to buy their silence. He insisted the settlement level was based on legal advice, or in the case of Clifford due to the ending of a wider contract.

James Murdoch also revealed he had authorised the settlements but had not told his father until 2009 after the case became public, saying the payments were too small to be reported to a higher board. He refused a request from MP Tom Watson to release Taylor from his confidentiality agreement.

Both James Murdoch and Rebekah Brooks, the former chief executive of NI who gave evidence later to the committee, said they had acted as soon as evidence emerged in civil cases at the end of 2010 that phone hacking had not been confined to Mulcaire and Goodman.

James Murdoch apologised for the scandal and told MPs: "These actions do not live up to the standards our company aspires to." The three came under pressure over a letter in May 2007 prepared by Harbottle & Lewis on the instruction of Jon Chapman, the former director of legal affairs, and Daniel Cloak, the head of human resources, suggesting phone hacking had not been widespread. The files on which the Harbottle & Lewis letter is based were re-examined in April by senior News International executives including Will Lewis, as well as Lord Macdonald.

In tense opening exchanges Murdoch revealed he had mounted no investigation when Brooks told parliament seven years ago that the News of the World had paid police officers for information. He said: "I didn't know of it." He also admitted he had never heard of the fact that his senior reporter at the News of the World, Neville Thurlbeck, had been found by a judge to be guilty of blackmail.

Watson interrupted to prevent Rupert Murdoch's son answering the questions, saying: "Your father is responsible for corporate governance, and serious wrongdoing has been brought about in the company. It is revealing in itself what he does not know and what executives chose not to tell him." Rupert Murdoch denied he was ignorant about his company, banging the table and saying News of the World was "less than 1%" of News Corp. He was asked about his connections to the Conservative party and revealed it had been on the advice of the prime minister's staff that he had gone through the back door to have a cup of tea with David Cameron after the election to receive Cameron's personal thanks for supporting his party in the election.

"I was asked if I would please come through the back door," Murdoch told the committee.

Rupert Murdoch denied that the closure of the News of the World was motivated by financial considerations, saying he shut the Sunday tabloid because of the criminal allegations. In one flash of anger he complained his competitors had "caught us with dirty hands and created hysteria".

Aware he must prevent the scandal spreading across the Atlantic, he said he had seen no evidence that victims of the 9/11 attacks and their relatives were targeted by any of his papers.

• This article was amended on 21 July 2011. The original stated that Lord Macdonald was on contract with News International and that he reported his findings to the News International board. This has been corrected.