Relatives of a private investigator who was killed with an axe 34 years ago are set to sue the Metropolitan Police over his unsolved murder.

Daniel Morgan died in the car park of the Golden Lion pub in Sydenham, south-east London, on March 10 1987, and a string of unsuccessful investigations into his death have been mired with claims of corruption.

In June this year an independent report accused the Met of institutional corruption over its handling of the case, saying it had concealed or denied failings to protect its reputation.

Met Commissioner Dame Cressida Dick apologised to Mr Morgan’s family, saying it was 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”.

On Monday, solicitor Raju Bhatt confirmed that a letter of claim had been sent to the force as Mr Morgan’s relatives fight to “achieve some semblance of accountability”.

In a statement the Morgan family said that while the 1,200-page report accurately reflected their experiences, they had since been disappointed by a lack of action by the Met, the Home Office, police watchdog the Independent Office for Police Conduct (IOPC) and the Mayor’s Office for Policing and Crime (MOPA ), which oversees the Met.

They said: “Three generations of our family have already suffered as the collateral damage resulting from the inexcusable failure of the institutions of the state to do what was required of them in the face of institutionalised police corruption.

“We do not want this burden to be passed on to the coming generations of our family.

“We want to be able to get on with our lives at long last, but that requires some form of acknowledgement on the part of those who have failed us.

“In all the circumstances, we consider we have been left with no option but to bring a civil claim against the Metropolitan Police in order to achieve some semblance of accountability.”

The panel that wrote the report, chaired by Baroness Nuala O’Loan, criticised Dame Cressida for initially denying it access to a police intelligence database.

Despite the controversy over the Morgan case, and other high-profile issues including the murder of Sarah Everard, in September it was confirmed that Dame Cressida’s contract had been extended by two years.

The Morgan family statement said: “We have been saddened – if not surprised – to find we have been let down yet again by all concerned.

“The present commissioner, Cressida Dick, felt able to simply reject the panel’s key finding of institutional corruption within the Metropolitan Police. Her role in obstructing the panel’s work – as detailed in their report – appears to have met with indifference and worse at the IOPC and MOPAC, where those charged with bringing her to answer for her role in this sorry state of affairs have shown themselves unable or unwilling to do so.

“And, in their wisdom, the Home Secretary and the London mayor deemed it fit to extend her term in office before the ink had dried on the panel’s report.”

A spokesman for the Met said: “We can confirm that the Metropolitan Police Service has received a letter of claim, dated 7 December, and is currently considering its response.

“Since the Daniel Morgan Independent Panel published its report six months ago, a dedicated team within the Met has been established and is progressing its response to those recommendations specific to the Met, while engaging with other lead organisations named in the report.

“We remain committed to this work and expect to fully report our progress to the Home Secretary and mayoral office in the spring 2022.”