The Metropolitan Police has been accused of "a form of institutional corruption" for concealing or denying failings over the unsolved murder of private investigator Daniel Morgan.
A report by an independent panel said the force's first objective was to "protect itself" for failing to acknowledge its many failings since Mr Morgan's murder, the panel's chairman Baroness Nuala O'Loan said.
Mr Morgan was killed with an axe in the car park of the Golden Lion pub in Sydenham, south-east London, on March 10 1987.
Despite five police inquiries and an inquest, no-one has been brought to justice over the father-of-two's death, with the Metropolitan Police admitting corruption had hampered the original murder investigation.
The Met owes Mr Morgan's family, and the public, an apology for not confronting its systemic failings and those of individual officers, the report said.
In a statement through their lawyer, the family of Mr Morgan said: "We welcome the recognition that we - and the public at large - have been failed over the decades by a culture of corruption and cover up in the Metropolitan Police, an institutionalised corruption that has permeated successive regimes in the Metropolitan Police and beyond to this day."
The Metropolitan Police said in a brief statement: “We deeply regret our failure to bring those who murdered Daniel Morgan to justice.” It said it was considering the report and would "respond in more detail" later on Tuesday.
The Independent Panel's report, which runs to more than 1,200 pages, expressed concern that within the Met "a culture still exists that inhibits both organisational and individual accountability".
It found: "The family of Daniel Morgan suffered grievously as a consequence of the failure to bring his family to justice, the unwarranted assurances which they were given, the misinformation which was put into the public domain, and the denial of failings in investigation, including failing to acknowledge professional competence, individuals' venal behaviour, and managerial and organisational failures.
"The Metropolitan Police also repeatedly failed to take a fresh, thorough and critical look at past failings.
"Concealing or denying failings, for the sake of the organisation's public image, is dishonesty on the part of the organisation for reputational benefit and constitutes a form of institutional corruption."
The initial investigation into Mr Morgan's death was heavily criticised, with the murder scene not searched and left unguarded, and no alibis sought for all the suspects.
A later probe by Hampshire Police, brought in to investigate amid fears of corruption, was compromised when a senior Met officer was appointed to work with the team, the report said.
The current Metropolitan Police Commissioner Dame Cressida Dick, was criticised for her refusal to allow the panel team access to the HOLMES police data system.
The report said: "The Metropolitan Police's lack of candour manifested itself in the hurdles placed in the path of the Panel, such as (then Assistant Commissioner) Cressida Dick's initial refusal to recognise the necessity for the Panel to have access to the HOLMES system."
The brother of Daniel Morgan said Ms Dick should "absolutely" be considering her position in light of the report.
Alastair Morgan was asked whether Ms Dick should consider resigning.
He responded: "Absolutely she should."
The family's solicitor Raju Bhatt added: "You heard from the panel that the institutionalised corruption that they found is a current problem in the present tense." The current leadership in the Met has to take responsibility for that continuing."
Baroness Nuala O'Loan, chair of the Daniel Morgan Independent Panel behind the report, said: "The family of Daniel Morgan has suffered grievously as a consequence of the failure to bring his murderer or murderers to justice, the unwarranted assurances which they were given, the misinformation which was put into the public domain, and the denial of the failings in investigation, including failing to acknowledge professional incompetence, individuals' venal behaviour, and managerial and organisational failures.
"We believe that concealing or denying failings for the sake of an organisation's public image is dishonesty on the part of the organisation for reputational benefit, and constitutes a form of institutional corruption."
Home Secretary Priti Patel, making a statement on the Daniel Morgan report, told MPs it is “devastating” that no one has been brought to justice 34 years after he was murdered.
She said: "The report sets out findings from its review of the last three decades, it's over 1,200 pages long and three volumes. It is right that we carefully review its findings.
"The report itself is deeply alarming and finds examples of corrupt behaviour - corrupt behaviour was not limited to the first investigation, that the Metropolitan Police made a litany of mistakes and that this irreparably damaged the chances of successful prosecution of Daniel Morgan's murder."
Asked if Prime Minister Boris Johnson still had full confidence in Dame Cressida during a Westminster briefing, his official spokesman simply replied: “Yes.”
In a statement released on Tuesday afternoon, Dame Cressida said she acknowledges the “extraordinary resilience and determination” of Mr Morgan’s family in their pursuit of the truth.
“It is a matter of great regret that no one has been brought to justice and that our mistakes have compounded the pain suffered by Daniel’s family. For that I apologise again now,” she said.
“I have been personally determined that the Met provided the Panel with the fullest level of co-operation in an open and transparent manner, with complete integrity at all times.
“I recognise this is a powerful and wide-ranging report. We will take the necessary time to consider it and the associated recommendations in their entirety.”