The Metropolitan Police said the “long time” it took for the family of a murdered private investigator to hear about documents relevant to the inquiry into his death is “regrettable”.

Daniel Morgan was killed with an axe 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 January 2023, documents relevant to the inquiry into his death were discovered in a locked cabinet in New Scotland Yard that had not been used for nine years, however, Mr Morgan’s family were not told until May 9, despite the Mayor’s Office finding out on April 24.

The Met’s Assistant Commissioner Louisa Rolfe told the London Assembly Police and Crime Committee on Wednesday: “The significance of these documents would not have been immediately apparent when they were discovered in January.

“And I think initial work was to work through the significance of the documents to work out and establish if they met the criteria for disclosure and sharing, because there were agreed protocols around the disclosure and sharing.”

She added: “Now of course, that long time delay between January and April and May is regrettable, and I appreciate the impact that might have had on trust.

“But in the context of the huge amount of material already shared, I think there was work in good faith to understand what is the nature of this information and how do we share it in the most appropriate way.”

A total of 95 pages of material should have been disclosed to the Daniel Morgan Independent Panel, which was set up to look into the case and published its final report in June 2021, the force said.

A further 71 pages were identified that would have been provided to His Majesty’s Inspectorate of Constabulary and Fire & Rescue Services (HMICFRS) as part of its subsequent inspection.

Committee member Caroline Pidgeon asked why the locked cabinet had not been checked before it was moved to New Scotland Yard from the old building in 2016.

She said: “I just don’t understand how that happened, let alone once you’re in there, nobody thought ‘we can’t open this cabinet, we need to check what’s in it’.

“You’re setting up a new office, how can it have just sat there in the corner on the management floor?”

Ms Rolfe responded: “I’m sorry, I can’t give an explanation for that at this time.”

Deputy mayor of London Sophie Linden told the committee: “Everybody’s just ‘how do you have a locked cabinet on the seventh floor that nobody knows what’s in it?’, it’s extraordinary.”

Asked about the time it took for her to be informed, she added: “Yes, it did worry me, and I did flag that as an issue that it had taken so long.”

Assistant Commissioner Barbara Gray apologised last month on behalf of the force to Mr Morgan’s family.

She said: “We fully acknowledge how unacceptable and deeply regrettable this situation is.

“We are working to understand what has taken place and any impact. We apologise to the family of Daniel Morgan and to the panel.”

The Met said its assessment found there are no evidential documents that relate to criminal investigations into the murder.

An independent panel set up to look into the case published a scathing report in June last year in which it accused the Met of “a form of institutional corruption” for concealing or denying failings over the unsolved murder.

In a statement, Mr Morgan’s family said last month they were “not surprised” by the news of the discovery.