A too-close relationship between senior Metropolitan police officers and sections of the media compromises the ability of both to investigate each other, an independent report in the wake of phone hacking has concluded.

Speculation that "cosy relationships involving excessive hospitality between some senior police officers and News of the World journalists" had undermined the police inquiry into hacking and "damaged trust in the impartiality of the police", it said.

The report, by former parliamentary commissioner Elizabeth Filkin, called for tighter controls over how the Metropolitan Police service deals with journalists to prevent erosion of trust in police not just among the public, but among police ranks.

Filkin, appointed in the wake of the Milly Dowler phone-hacking revelations in July 2011, said the most serious problem was that "that the close relationship between some senior members of the Met and some sections of the media compromises the capacity of both those institutions to scrutinise the activities of the other".

Lack of transparency about the nature of the relationship between police and media also led to speculation and perceptions, whatever the facts, that caused "serious harm".

The report quotes Adrian Lee, Northants chief constable and the Association of Chief Police Officer's lead on professional ethics, saying: "If you ask yourself the question, not just 'Are we right?' but 'Are we seen to be right?' then we failed the test on the News International scenario.

"In terms of being close to News International, we were investigating them. The perception is that the investigation is linked to our good relationship. We haven't done enough to give the public confidence that the two things aren't linked."

Contact between the MPS and the media had "not been transparent enough", which had led to "a lack of trust internally" the report said.

There was also "lack of consistency" in how some of the MPS senior team viewed gifts and hospitality. MPS deputy assistant commissioner Mark Simmons told Filkin the perception in the lower ranks was "that the bosses are filling their boots".

Welcoming the report, titled Ethical Issues Arising from the Relationship Between Police and Media, Met commissioner Bernard Hogan-Howe pledged an "open and transparent" relationship with media.

"There should be no more secret conversations," he said. "There should be no more improper contact. By that, what I mean is that which is of a selfish rather than public interest.

"Meetings will no longer be enhanced by hospitality and alcohol. That doesn't mean to say there will never be an occasion when we take hospitality with journalists. But on the whole we wouldn't expect to see it."

The Met's Directorate of Professional Standards will investigate any unauthorised disclosure of information, he said. "Anyone found to have improperly shared information will be subject to misconduct and/or criminal proceedings. We need to be open about our contact with the media."

Other salient points in the report included:

• A "change of culture" was needed at the MPS, and Filkin recommends that two new senior positions be created – that of public information, and integrity and ethics champions.

• In guidance to police officers, Filkin warns of the danger of flirting and drinking with journalists. Drinking with officers "may be seen as inappropriate hospitality," her report said. "Mixing the media with alcohol is not banned, but should be an uncommon event. She urges officers to watch out for "late-night carousing, long sessions, yet another bottle of wine at lunch – they are all longstanding media tactics to get you to spill the beans. Avoid".

• The perception that the MPS leaks information to the media is " prevalent and damaging", she said. In a bid to tighten up unauthorised leaks, officers should make a personal record of any information they pass to journalists, with those records open to a random audit. If leaks did not lead to criminal proceedings, then "robust" management action was required.

The report advocated more communication, not less, with the media, but in a controlled way. There was a "range of contact that is 'not permitted' and which, if unregulated, will continue to cause damage to the MPS and the public", she said.

"The events of July 2011 [when the Guardian reported that Milly Dowler's phone had been hacked by the News of the World] have demonstrated that vigorous and fearless responsible journalism is vital for public interest.

"In my view the MPS needs to be more open and active in responding to responsible requests for information to improve its accountability to the public. The MPS should never be in the business of providing information or stories to reduce scrutiny."

Filkin was called in by former Met commissioner Sir Paul Stephenson to conduct the inquiry. He resigned in July amid allegations about the force's PR contract with Neil Wallis, the former deputy editor of the News of the World, who was later arrested on suspicion of phone hacking.

Issues arising from the Guardian's July revelations had so far cost the MPS more than £3m in cost of subsequent inquiries, the loss of senior staff and other unforeseen consequences, said the report.