Police have launched a full investigation into allegations that Conservative politicians were involved in a paedophile ring at a guest house in the 1980s.
Operation Fernbridge will look into historical child abuse claims at Elm Guest House in Barnes, southwest London.
It is alleged children who were living at Grafton Close children's home in nearby Richmond were taken to the guest house and sexually abused by a number of "prominent people", including Tory MPs. Met police confirmed no current occupants of Elm Guest House, which is now a private residence, are connected to the allegations.
Police launched an investigation after they were given information by Tom Watson, Labour MP for West Bromwich East.
Speaking under parliamentary privilege in the Commons in October, Watson urged police to re-investigate evidence against former consultant to the National Children's Bureau and convicted paedophile Peter Righton.
Watson claimed the evidence file on Righton contained "clear intelligence of a widespread paedophile ring", adding: "One of its members boasts of a link to a senior aide of a former Prime Minister, who says he could smuggle indecent images of children from abroad.
"The leads were not followed up, but if the files still exist, I want to ensure that the Metropolitan Police secure the evidence, re-examine it, and investigate clear intelligence suggesting a powerful paedophile network linked to Parliament and No 10."
Working in secret under the codename Operation Fairbank, five officers on the Metropolitan Police's Child Abuse Investigation team began a scoping exercise to see if Watson's claims demanded a full inquiry.
Scotland Yard has now confirmed Watson's claims had "reached the threshold for a criminal investigation."
In a statement, Scotland Yard said: "The Metropolitan Police Service has today launched an investigation, Operation Fernbridge, into historic allegations of child abuse in the early 1980s at the Elm Guest House, Rocks Lane, Barnes, London.
"The investigation will be led by the Child Abuse Investigation Command.
"The allegations under Operation Fernbridge were initially assessed under Operation Fairbank which was information passed to police by MP Tom Watson. Operation Fernbridge reached the threshold for a criminal investigation.
"We will not be providing a running commentary on this inquiry."
Following the announcement, Tom Watson said: "This new criminal investigation is welcome news. I am confident that the Operation Fairbank team are committed to a thorough investigation that leaves no stone left unturned.
"As they get nearer the truth it is vital they are given the time and space to conduct the investigation without interference.
"I urge any witnesses or victims to come forward if they think they can help with the inquiry.
"No matter what has happened in the past, now is the time for your voice to be heard."
Anyone with information is asked to contact officers on 020 7161 0500.