A police investigation into an Essex paedophile ring was mysteriously shut down just as key intelligence was coming in, secret files suggest.

The records also prove that a generous plea bargain given to the ringleaders freed them to abuse many more children.

Essex Police and the National Police Chiefs Council (NPCC) tried to withhold the documents, but a precedent-setting Freedom of Information battle by the Archant Investigations Unit forced their disclosure.

The unit's award-winning true crime podcast 'Unfinished: Shoebury's Lost Boys' has now released two new episodes exploring more than 1,000 pages of confidential police files.

They shed new light on Southend-based ringleaders Dennis King and Brian Tanner, who trafficked victims to locations including Havering and Tower Hamlets.

The duo, both now dead, were convicted in 1990 of running what the authorities dubbed “the Shoebury sex ring” - but a plea deal saw their predicted sentences of 15 years to life reduced to just three and four years.

Last year, Unfinished reported on evidence that King was a registered police informant linked to Lennie Smith, a suspect in the killings of Jason Swift, Mark Tildesley and Barry Lewis.

The new documents, spanning eight decades, have unearthed even more dark secrets.

Here are some of the biggest revelations:

King and Tanner were offending together for over 10 years

Essex Police files revealed that in 1980, Tanner was prosecuted for paying a victim to lie in court.

The podcast tracked down that victim, who said he had been abused not just by Tanner but by King as well.

He had “no idea” why only Tanner was prosecuted.

Files subsequently disclosed by the NPCC confirmed police had already listed King and Tanner as criminal associates in 1978.

They were not jointly prosecuted until 1989.

Their generous plea deal freed them to abuse more children

Previous episodes of Unfinished revealed how Dennis King had left prison, moved to Peterborough and spent another two decades abusing children.

NPCC files have now shown Tanner also reoffended.

In 1998, he was convicted in Northampton of abusing teenage boys and possessing a hoard of child pornography.

Campaigners say that had the men been sentenced appropriately in 1990, they would have still been behind bars, unable to prey on more victims.

Loss of police records may have blocked justice

Essex Police files showed several complainants came forward in 2016, when a modern-day review was launched into the old case.

One of them claimed he had reported his abuse to police at the time.

But all of the force's paper records from the original case had been lost or destroyed.

This meant the man's past account and his more recent account could not be compared, so bringing charges could be argued to be an "abuse of process".

Whistleblower Robin Jamieson – the former head of the Southend NHS psychology department, which treated several of the victims – condemned the revelation as “shocking”.

An investigation into the ring suddenly ended without explanation

The only records police could find from 1989/90 were ten A4 pages of brief police computer entries showing that after King and Tanner’s sentencing, police had opened a new investigation into the wider ring.

Officers were probing contacts of King and Tanner, in locations including Barking.

On July 31, 1990, they received intelligence that King had been paid a weekly retainer by somebody higher up in the ring.

They were also told children had been solicited to appear in pornographic films and were given the names of witnesses who could allegedly corroborate this.

But days later, all computer activity in the case suddenly stopped, the reason for which remains shrouded in mystery.

What the police say

Essex Police said that in 2016, “specialist detectives from our Child Abuse Investigation Teams carried out extensive enquiries, interviewing numerous witnesses and victims.

“As a result of our review, in April 2017, a further allegation of non recent child abuse was reported. Sadly, despite extensive investigation, this has not resulted in criminal charges.”

It urged anybody with information to contact police on 101 or online, or call Crimestoppers anonymously on 0800 555111.

*All 11 episodes of Unfinished: Shoebury’s Lost Boys are available on your usual podcast provider or by visiting www.podfollow.com/unfinished-1/

Alternatively, listen to them below:

For more, read:

Essex police officers face action after investigator finds 'inexcusable' failures in paedophile ring case

What happened when police reopened an investigation into an Essex paedophile ring?

True crime podcast investigates claims that Essex paedophile ring victims were failed