Four senior officers will appear before Commons committee to salvage tarnished reputation of the Metropolitan police

Police chiefs will try to stanch the battering to the Metropolitan police's reputation caused by the phone-hacking scandals by telling a powerful committee of MPs that mistakes had been made, but they were the result of cock-ups and confusion and not the sign of any conspiracy.

The home affairs committee resumes its hearings on Tuesday into phone hacking with four past and present Scotland Yard chiefs.

First up is assistant commissioner John Yates, who will tell MPs that he did not examine any documents before declaring in 2009 that the Met did not need to reopen its phone-hacking investigation, which had closed two years earlier after gaining two convictions.

Yates appears before MPs on a crucial day for Britain's biggest police force, who are under fire for missing numerous allegedly criminal acts of phone hacking by the News of the World, and for some of its officers allegedly selling information to the paper which facilitated the hacking of the royal family.

A concerted Yard fightback saw Yates acknowledge to the Sunday Telegraph that his 2009 decision was "pretty crap" and admit mistakes, followed on Monday by the Met accusing News International of leaking to try to derail its corruption investigation.

Tuesday's hearings, police chiefs will hope, will at least not add to the damage. They hope the flood of revelations about the police will then begin to dry up.

In a letter to the committee released on Monday, Yates said the failure to detect the hacking of Milly Dowler's phone was "a source of great regret".

He denied ever having said he had "reviewed" the Met's phone-hacking investigation following revelations in the Guardian in July 2009. Yates, in his letter to MPs, said he talked to the head of the 2006/7 inquiry: "Following detailed briefings from the senior investigating officer, it was apparent that there was no new material in the Guardian article that would justify either reopening or reviewing the investigation. A short while later, this view was endorsed independently by the director of public prosecutions, Keir Starmer QC.

"Therefore, as can be seen, in relation to events that took place in 2009, I was provided with some considerable reassurance (and at a number of levels) that led me to a view that this case neither needed to be reopened or reviewed."

But prosecution sources indicated they do not agree. A source said the Crown Prosecution Service's view was still that "the legal advice given by the CPS to the Metropolitan police on the interpretation of the relevant offences did not limit the scope and extent of the criminal investigation", as contained in a letter in April by Keir Starmer to MPs on the culture, media and sport committee.

Yates's previous sessions before MPs have been tetchy affairs. Labour MP Tom Watson used parliamentary privilege to attack Yates: "John Yates's review of the Mulcaire evidence was not an oversight. Like Andy Hayman, he chose not to act, he misled parliament. He misled readers of the Sunday Telegraph only yesterday."

Last night, Watson told BBC Newsnight: "He should resign with dignity." Tory MP George Eustice also said he no longer had confidence in Yates.

Bob Milton, a Metropolitan police commander between 1999-2003 who headed the Special Branch protection squad and was in charge of security vetting for officers at the level of national security, also gave Yates less than enthusiastic backing.

"John Yates is a very, very competent police officer. He has admitted that perhaps he had a lack of judgment two years ago. He will have to make his own decision as to whether he feels that his own position is untenable," he said on Newsnight.

Asked what his own view was, Milton replied: "It depends why he made the decision. If he made it on operational grounds, then fair enough. If for any other reason he was influenced in any other way, then he should step down."

Also before the committee today is former assistant commissioner Andy Hayman, who is expected to say he had limited involvement in the decision-making when the royal household contacted police over concerns their mobile phones may have been hacked. The investigation was handled by specialist operations, which include royal protection but also houses the counter terrorism command.

The 2006 investigation is accepted by the Met to have been too limited in its scope, failing to inform scores of victims, although it led to the conviction in 2007 of a News of the World reporter and a private investigator.

After leaving the Met over controversy about his expenses, Hayman wrote occasional columns about policing for the Times, which is also owned by News International.

Also before the committee will be former counterterrorism chief Peter Clarke. Hours after the 2006 arrests were made over phone hacking, police had to arrest alleged plotters in the biggest terrorism plot ever uncovered in Britain, which saw people convicted of planning to explode liquid bombs aboard planes heading from London to north America.

Sue Akers, head of the current hacking inquiry, will also testify, though the need not to compromise the investigation will restrict the scope of her answers.

The position of Met commissioner Sir Paul Stephenson also looks rocky, says Chris Boothman, a lawyer and independent member of the Met authority, which supervises the service: "I don't think the commissioner's position is safe. This is about the management and supervision of the police service. No one has the power to intervene in the way investigations are run, so the buck stops with the commissioner. If there have been failings, the commissioner has to take responsibility for it."

Last night the New York Times claimed that five senior Met officers discovered their mobile phone messages had been targeted shortly after Scotland Yard began its initial phone hacking inquiry in 2006.

"If it is true that police officers knew their phones had been hacked, it is a serious matter that requires immediate investigation," said ToryMP John Whittingdale, chairman of the culture, media and sport committee, which investigated phone hacking. "It would be shocking."

The Guardian also understands the Independent Police Complaints Commission plans to take over Scotland Yard's investigation into allegations that its officers were paid by the News of the World. The Independent Police Complaints Commission has confirmed that it will assert its authority over the Metropolitan police "as and when" the force identifies individual officers suspected of receiving bribes.