The serial killer drugged his victims Anthony Walgate, Gabriel Kovari, Daniel Whitworth and Jack Taylor with overdoses of GHB and dumped their bodies near his flat in Barking, east London, between June 2014 and September 2015.

Despite what many now see as the obvious links between these deaths, it wasn't until the final victim's body was found, with the grieving families carrying out their own investigations, that local police finally realised they had a serial killer on their hands.

A new report by His Majesty's Inspectorate of Constabulary and Fire and Rescue Services (HMICFRS) has warned the more junior officers who are often sent to investigate "sudden deaths" - which happened in the Port case - are still "inexperienced, untrained and poorly supervised."

HMICFRS highlighted problems with oversight and supervision, unacceptable record keeping, confusing policy and guidance, and inadequate intelligence and crime analysis as reasons for the flawed investigations.

His Majesty's Inspector of Constabulary, Matt Parr, told Sky News that, to this day, they continue to see worrying signs of inept policing in the early stages of an investigation.

He said that once a death is established as a homicide, the Metropolitan Police have some of the best detectives in the country to investigate - but before that, the standards are much lower.

"If they get the basics wrong right at the start, the chances of categorising the cases wrongly and therefore the danger of something like Stephen Port happening again goes up.

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"It's entirely possible [they will have missed another serial killer].

"If you look at the number of deaths that get reported to the Met, I don't find it unrealistic to think some of those that they write off are probably homicides."

Mr Parr also spoke about seeing a lack of "professional curiosity" and laziness from officers, and said spotting links between cases was more reliant on "luck."

"Several officers told us that linking deaths at a local level relied frankly on luck, there was no formal process to spot the similarities, to link deaths, and it relied on officers maybe talking to each other about the deaths that they've dealt with. We find that extraordinary."

'Most basic' checks not being carried out

They also found examples of the "most basic" checks not being carried out during investigations.

This included poor documentation, key details like race not being routinely recorded on police death reports, and insufficient searches.

In some cases, vital evidence was only discovered when a body was taken to a mortuary because officers had "not even looked in the pockets" of somebody found dead, Mr Parr said.

All of this has led the Inspectorate to conclude a tragedy such as the Stephen Port case could happen again.

"The most challenging question for us to answer is whether events like these could happen again. History and the findings of this inspection tell us that they will," Mr Parr said.

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Inspectors have made 20 recommendations for the Met, which include increasing the use of intelligence by officers responding to deaths and improving family liaison in unexpected death cases.

Inspectors also considered whether homophobia explained the failings, but said it was "impossible to reach any definitive conclusions".

Mr Parr said: "No-one's denying that there are homophobic officers in the Met", referring to Baroness Casey's report which found the force to be institutionally racist, sexist and homophobic.

But the officers "didn't even realise that these were four young gay men at the start so the failings are all just about, I think, a lack of professionalism and a lack of expertise across the board in the way that they deal with unexplained deaths", he warned.

Fight continues for public enquiry

The sister of Port's final victim, Jack Taylor, welcomed the report but called for real change and accountability.

Donna Taylor said: "We've not been able to grieve for Jack because all we've ever done is have to fight, fight, fight and we're still fighting to this day for a public inquiry.

"We're still fighting for justice and for someone to stand up and show some accountability."

The force has apologised for failing the victims and their families - and vowed to carefully consider the recommendations in the report.

Met Police Assistant Commissioner Louisa Rolfe said: "The deaths of Anthony Walgate, Gabriel Kovari, Daniel Whitworth and Jack Taylor were a tragedy and we are sincerely sorry we failed them and their families.

"While, as the inspection report acknowledges, we have worked hard since the murders to understand what went wrong and improve how we work, it highlights more we need to do.

"We have to get the basics right. That's around how we train and support our officers to investigate deaths, identify suspicious circumstances and understand how protected characteristics may impact on those investigations.

"Our death investigation policy is sound, now it's about turning policy into effective practice. To do this we have reviewed and updated our training for frontline officers and have begun a programme of enhanced training for their supervisors.

"We are also moving quickly on family liaison. We know we fell short in this case and the families did not get the service they needed or deserved. It is important we look again at this area to see what more we need to do to support families through such difficult times.

"We will fully consider the recommendations made by HMICFRS and ensure these are not just fully addressed but embedded into our working practices. This is what we have been doing with previous recommendations from the Coroner and the Independent Office for Police Conduct.

"We are sincere in our desire to make real change to minimise the chance of a case like this ever happening again."