London (CNN) -- British police have arrested a couple on suspicion of holding three "extremely traumatized" women captive for more than 30 years, Scotland Yard announced Thursday.
One of the women -- a 30-year-old Briton -- "appears to have been in servitude for her entire life," Metropolitan Police Detective Inspector Kevin Hyland said. She and the other two women, a 57-year-old from Ireland and a 69-year-old from Malaysia, have been taken to a place of safety and are being cared for by a charity, police said.
The man and woman arrested are both 67, police said. They were taken into custody at their home in the south London borough of Lambeth and were being held as part of an investigation into slavery and domestic servitude, police said.
Their names were not released, and police said only that they are not British nationals. They were later released on bail.
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," he 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." 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."
A television documentary on forced marriages relating to the work of Freedom Charity prompted one of the victims to call for help. 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."
News of the couple's arrest first spread on Twitter.
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."
The women had "some controlled freedom" during their captivity, Hyland said. Investigators have 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."
UK Special Envoy for Human Trafficking Anthony Steen told CNN he was not surprised 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.