LONDON — Scotland Yard detectives believe that an organized pedophile ring at the heart of the British establishment was responsible for the murder of three young boys and the violent sexual abuse of dozens more.

A survivor, known as Nick, described regular “abuse parties” that were held at a luxury apartment block near Westminster during the premiership of Margaret Thatcher. He said he watched a Conservative Member of Parliament strangle one boy to death, and witnessed another young boy brutally murdered in front of a Cabinet minister.

Detective Superintendent Kenny McDonald, who is leading an investigation of the alleged “VIP” abuse network said today: “I believe what Nick is saying to be credible and true.”

Nick says children between the ages of seven and 16 were taken to the events, including regular Christmas parties, which were often held at Dolphin Square, an exclusive building on the River Thames that was popular with MPs who needed second homes in London close to the Houses of Parliament. He has described the partygoers as a cross-section of some of the most powerful men in Britain including Sir Peter Hayman, a long-time MI6 chief.

Perhaps the most shocking of Nick’s allegations concerns a Conservative MP accused of murdering a boy, who looked about 12 years old, during a sadistic sex game in 1980. He claimed that he and the brown-haired boy were collected in a chauffeur-driven car and taken to a town house in Central London for one of these “abuse parties”, where members of the military, law enforcement and political establishment would give glasses of whiskey to the children before violating them.

Speaking to the investigative journalism website Exaro, Nick gave a graphic account of the way the MP sexually assaulted and then strangled the child to death. “I watched while that happened. I am not sure how I got out of that,” he said.

Nick said he had witnessed a second boy being beaten so savagely by two men at one of the parties that he succumbed to his injuries and died, while a serving member of the Thatcher government watched on. He alleges that a third boy, aged 10 or 11, was deliberately hit by a car and killed by a member of the pedophile network in 1979.

The extraordinary allegations were first made public earlier this year by Exaro, which agreed to maintain the victim’s anonymity. He subsequently asked a reporter to accompany him as he dared to share his story with the police for the first time.

On Thursday, Detective Superintendent McDonald described his account as “harrowing” and compelling. “Nick has been spoken to by experienced officers of the child abuse team and experienced officers from the murder investigation team. They and I believe what Nick is saying,” he said.

“He has outlined how organized the abuse was. How a car would be sent to collect him and he would be taken somewhere. The abuse he was subjected to was carried out by a man acting alone or a group of men or even what can only be described as parties… Today I want to appeal directly to those other young boys, now men, who were also subject to abuse at the hands of these men. I believe that there were other boys who were abused, or who were present whilst the abuse took place.”

Nick, and another survivor who has spoken to Exaro allege that policemen and senior security officials were among the abusers, giving the impression that they were acting with impunity.

A Scotland Yard inquiry has been established to investigate whether the Metropolitan Police was guilty of overlooking the crimes of powerful figures, or whether some kind of cover-up operation was in place.

Over the years, several MPs have alleged cover-ups or suggested that investigations were shut down by senior security officials. In 1981, Sir Peter Hayman, a former diplomat and intelligence operative, was outed by Conservative MP Geoffrey Dickens, who used Parliamentary privilege to name him as a pedophile in the House of Commons. Dickens continued to investigate the pedophile ring, which he claimed included “big, big names,” and he passed a 40-page dossier of evidence to the Home Secretary in 1983.

Dickens claimed his name subsequently appeared on a hit-list and his house was broken into by burglars who scoured his office but never stole any possessions. “The noose around my neck grew tighter after I named a former high-flying British diplomat on the Floor of the House. Honorable Members will understand that where big money is involved and as important names came into my possession so the threats began,” he told the House of Commons in 1985.

No criminal charges ever came from the evidence he raised. Last year, the Home Office said the dossier had mysteriously disappeared from the archives.

Current Labour MP John Mann has suffered no personal threats but says his investigation into allegations of a VIP pedophile network were also shut down by the authorities. As a local politician in Lambeth, South London, he said he became aware of allegations that young boys in care homes were being recruited as rent boys and taken to Dolphin Square. “We were told this by several sources. It was very specific: there were sex parties there, and they involved Tory MPs,” he told the Daily Mail last month.

He passed the information to the police who came back to him after three months to apologize and say they had been instructed to stop looking into the abuse parties. “They'd been forced to drop it,” Mann said. “Pressure had come from on high in the police service.”

A former senior detective at the Metropolitan Police, Clive Driscoll, said earlier this year that he had been hastily removed from an investigation that had begun in Lambeth into child abuse when his superiors saw a list of suspects, which included several MPs, that he wanted to investigate. He said he thought his investigation was “too uncomfortable.”

Steve Rodhouse, Deputy Assistant Commissioner of the Metropolitan Police, said on Thursday that an inquiry was underway to address allegations that police officers had acted inappropriately in relation to child abuse allegations, including the claims made by Driscoll. "Clive has had a fantastic and distinguished career so we listen to what he has to say," he said.

The investigation into an alleged cover-up is just one of 18 strands of inquiry currently ongoing as part of Operation Fairbank, which was first set up in 2012 into allegations of a VIP pedophile ring. One of those concerns Nick’s more recent allegations about Dolphin Square, another involves allegations against Cyril Smith, a Liberal MP who died in 2010. Twenty men have come forward to claim they were abused as boys by Smith, who was investigated numerous times during a three decade career but was never charged with any crime.

In total, officers said 600 emails or tip-offs had been received by more than 40 officers working on Operation Fairbank. Thus far, just five people have been arrested.