London (CNN) -- British police have arrested a couple on suspicion of holding three women captive for more than 30 years, Scotland Yard announced Thursday.
Officers from the Human Trafficking Unit arrested the man and woman, both 67, at their Lambeth, south London home early Thursday as part of an investigation into slavery and domestic servitude, the Metropolitan Police said. They are in custody.
The "highly traumatized" victims -- a 69-year-old Malaysian woman, 57-year-old Irish woman and 30-year-old Briton -- have been taken to a place of safety and are being cared for by a charity, the Metropolitan Police said.
Police said they'd been alerted in October to the situation by Freedom Charity, which got a phone call from a woman saying "she had been held against her will in a house in London for more than 30 years."
"We have launched an extensive investigation to establish the facts surrounding these very serious allegations," Detective Inspector Kevin Hyland said.
"We've established that all three women were held in this situation for at least 30 years. They did have some controlled freedom."
Hyland praised the actions of Freedom Charity and said police were working with the organization to support the victims.
"They are extremely traumatized, which explains the discrepancy between when the Freedom Charity were contacted and the arrests were made," he said. "It would be wrong of us to move at a pace that would further traumatize any victims."
Hyland said police were unsure where the youngest victim had been born, "but she appears to have been in servitude for her entire life."
Police had seen no evidence of sexual abuse, he said. "We're very early in the investigation, we're not investigating offenses of a sexual nature, there haven't been any arrests of a sexual nature, so that's the circumstances at the moment."
Hyland said it was an unprecedented case for the Met's Human Trafficking Unit: "We've seen some cases where people have been held for up to 10 years, but we've never seen anything of this magnitude before."
A television documentary on forced marriages relating to the work of Freedom Charity prompted one of the victims to call for help.
Freedom Charity spokeswoman Aneeta Prem said the organization had taken "immediate action" to plan a rescue after learning of the women's situation.
"Facilitating their escape was achieved using utmost sensitivity and secrecy and with the safety of the women as our primary concern," she said, describing the work of those involved as "outstanding."
CNN's Max Foster said police had told him that the women had been released in October after sensitive negotiations by the charity.
The charity had worked to gain their trust and coax them out of the house, communicating through prearranged phone calls.
"Over time they built up that trust, the police gathered outside the house and then they had the confidence to leave the house," Foster said. "It seems to have taken place in a suburban area of south London, in an ordinary street."
UK Special Envoy for Human Trafficking Anthony Steen told CNN he was unsurprised by the case as there were likely to be many cases of domestic slavery in the country.
"We don't know the number but we know it's pretty huge. Domestics are hidden away," he said.
"The difference between slavery when it was manifest in America -- as it was in England -- was that you could see it everywhere," Steen said. "Since then having abolished it, it's grown, it's got bigger and bigger -- in fact they say it's between 10 and 20 times the size it was in the 1800s."
Steen said the largest number of people involved in slavery in Britain were in brothels, and that group was followed by men held against their will in debt bondage.
CNN's Max Foster in London contributed to this report.
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