Scotland Yard also believe abuse took place in London and Home Counties - and are also probing abuse at military bases

Police yesterday described claims that a Conservative MP strangled a boy of 12 as ‘credible and true’.

Officers investigating three alleged murders linked to a VIP paedophile ring also backed claims that a Tory minister watched as another boy was murdered.

Scotland Yard has now launched an extraordinary appeal for information from celebrities, politicians and foreign dignitaries who lived at or visited the exclusive Dolphin Square estate in central London in the 1970s and 1980s.

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Scandal: The Met is looking into explosive claims boys were abused and even killed by Conservative politicians at Dolphin Square, a block of flats in Pimlico, London

It comes after months of Daily Mail investigations concerning alleged abuse at Dolphin Square and the nearby Elm Guest House in south-west London.

Detectives say they believe a witness who claimed he was sexually assaulted at Dolphin Square, in Pimlico, by senior MPs, spies and prominent military figures during ‘abuse parties’ over a period of almost a decade.

The alleged victim, known only as Nick, says he was molested from the age of seven to 16. He has told how he saw a Conservative MP strangle a 12-year-old boy at an orgy in a London townhouse around 1980, and that a Conservative Cabinet minister watched two men kill another boy in a depraved sexual assault a year later.

A third boy aged ten or 11 was deliberately run over in broad daylight in south-west London by an unknown member of the paedophile gang in 1979, he alleges.

THE WHISTLEBLOWER: MAN AT CENTRE OF THE INQUIRY The man at the centre of the Dolphin Square inquiry says he was abused at depraved sex ‘parties’ from the age of seven. Known only by the pseudonym Nick, he claims to have witnessed horrific acts at the luxury estate in central London between 1975 and 1984. After being abused by his father, Nick says he was handed to a gang of top Establishment figures. He has described being driven by a chauffeur, along with a terrified 12-year-old boy, to a luxury townhouse where he watched as a Tory MP strangled the other child. Nick also said he saw a second boy being brutally murdered in front of a Tory Cabinet minister in 1981. A third boy, aged ten or 11, had died in 1979 after being deliberately run over by a member of the paedophile gang in a ‘warning’ to victims not to speak out, he alleges. He says he was taken to Dolphin Square at least ten times for ‘abuse parties’. He claimed one MP told him to thrash another boy - and ‘sexually punished’ him when he refused. After receiving counselling he contacted the investigative website Exaro in May, whose investigators described him as ‘intelligent and articulate’, before going to the police. Advertisement

Police have now appealed for potential witnesses who lived in or visited Dolphin Square, where Nick said the majority of the abuse took place, between 1975 and 1984.

They confirmed for the first time they were looking at ‘allegations of serious and organised sexual abuse’ at Dolphin Square and other locations, including military bases, after Nick said he and several other boys were driven to properties in London and the Home Counties, where they were raped, cut and beaten.

Now in his forties, Nick has helped to compile e-fits of the three alleged murder victims, whose names he never learned.

Police are working through historical missing persons reports and unsolved child murders to look for possible matches.

Detectives have spoken to the family of Martin Allen, who disappeared in 1979 aged 15, but are not currently linking him to Dolphin Square. Similarly, Sussex Police is reviewing the disappearance and murder of eight-year-old Vishal Mehrotra in 1981. The Royal Military Police is also investigating claims that military bases were used by a VIP paedophile ring.

Scotland Yard first launched its investigation into Nick’s claims – Operation Midland – last month.

Detective Superintendent Kenny McDonald said: ‘Nick has been spoken to by experienced officers from child abuse teams and experienced officers from murder investigations. They and I believe what Nick is saying is credible and true.’

He continued: ‘There will be people who lived at, or visited, Dolphin Square from the early 1970s onwards who will have seen or heard something that they only now understand the significance of.

Today I would like to ask former residents, current residents, or anyone who routinely went to Dolphin Square to think back and get in touch with us with any information they may have.’

The luxury estate has long been home to politicians, foreign dignitaries, and stars of stage and screen – as well as spies and glamour girls.

Famous former residents include Harold Wilson and William Hague; Christine Keeler and Mandy Rice-Davies, key players in the Profumo Affair; and Sir Oswald Mosley, founder of the British Union of Fascists.

Mystery: Police officers in Sussex are reviewing the disappearance and murder of eight-year-old Vishal Mehrotra (left). Right, his father Vishambar Mehrotra

Other venue: The Elm Guest House in South-West London, above, was frequented by VIPs and politicians where it is believed they abused vulnerable children

According to Nick, the estate also hosted sordid ‘parties’, where children were plied with whisky after being escorted from school.

Unsolved: Martin Allen, 15, disappeared in 1979

Det Supt McDonald said: ‘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 would ask you to trust me. I will support you, and do everything in my power to find those responsible and bring them to justice.’

Operation Midland falls under a wider umbrella of investigations, Operation Fairbank, exploring allegations of child abuse by VIPs. One of the most high-profile strands is Operation Fernbridge, concerning Elm Guest House.

Tom Watson, the Labour MP who warned in Parliament two years ago that a paedophile ring was linked to No 10, said: ‘It will come as a great relief to Nick that his allegations are being fully investigated and taken seriously ... now is the time for any victims to speak to the police.’

Yesterday police also said they are probing claims that officers acted inappropriately in relation to child abuse probes from the mid-1970s until as recently as 2005.

Last July it emerged that a dossier compiled by Geoffrey Dickens, naming Cyril Smith and other suspected Establishment paedophiles, had vanished after it was sent in 1983 to the then home secretary Leon Brittan. A recent Home Office inquiry failed to uncover the file, and Theresa May said she could not rule out a possible cover-up.

The Government has planned an inquiry into the claims of a VIP paedophile ring – but is struggling to find a chairman.

Lawyer Fiona Woolf and retired judge Baroness Elizabeth Butler-Sloss were both appointed but later had to step down due to their links to the Establishment.