Commander Steve Rodhouse of Scotland Yard police said detectives were trying to understand the “invisible handcuffs” used to control the women, including a 30-year-old who had spent her entire life in servitude.
“What we have uncovered so far is a complicated and disturbing picture of emotional control over many years,” Rodhouse told reporters.
“Brainwashing would be a simple term but I think that belittles the years of emotional abuse these victims have had to endure.”
He also revealed that the two suspects in the case, a man and a woman both aged 67 who were arrested at a house in south London on Thursday, had been detained before, in the 1970s, but gave no further details.
Accused of involvement in forced labour and domestic servitude, as well as immigration offences, the pair -- who are both foreign nationals -- have been bailed until January pending further investigations.
Their passports have been confiscated and they are not allowed to return to the house.
Rodhouse said the case was “unique”.
The women were rescued on October 25, one week after first making secret telephone contact with a charity.
They are a 69-year-old Malaysian, a 57-year-old from Ireland and the 30-year-old Briton.
Detectives do not believe the women were sexually exploited or had been the victims of human trafficking, but they have reported what they called “beatings”.
“It is not as brutally obvious as women being physically restrained inside an address and not being allowed to leave,” said Rodhouse.
Explaining the gap between the liberation of the women and the arrests of the two suspects, police said they had to be patient in trying to understand the women’s accounts.
In Thursday’s raid in the borough of Lambeth, the suspects’ address was searched for 12 hours. Some 55 bags of evidence were seized, amounting to more than 2,500 exhibits.
All 37 officers in Scotland Yard’s Human Trafficking Unit (HTU) -- which deals with modern-day slavery cases -- are working on the investigation.
Specially-trained officers are working with the women to try and understand their lives.
“This may take weeks, or many months,” said Detective Inspector Kevin Hyland, who heads the unit.
He said officers did not believe the case was linked to any other groups and were not looking for further victims.
“There is nothing to suggest that the suspects were violent to others outside of the address,” he added.
Scotland Yard is in touch with the Malaysian and Irish embassies but officers would not disclose if they had discussed names with the missions.
Hyland said that during their captivity the women had been able to leave the house in carefully-controlled circumstances but had “no real exposure to the outside world”.
The case has sparked national soul-searching amid fears it is the tip of an iceberg.
Aneeta Prem, the founder of the charity which helped the three women in London, said their plight had already prompted other people to come forward in the 24 hours since it was revealed.
The women, who are now being cared for in an unspecified location, were rescued after the Irish woman “found the courage” to call the Freedom Charity on October 18 after seeing their work in a television programme.
The charity normally deals with forced marriage and honour-based abuse, so is used to working with women who feel trapped in difficult domestic situations.
After secret telephone calls, the British and Irish women agreed to meet charity workers and police outside the house, before taking them back to the property to rescue the Malaysian.
Prem said of the moment when she met them: “They all threw their arms around me, and apart from crying enormously, they thanked the charity for the work Freedom had done in saving their lives.”
James Brokenshire, a junior Home Office minister, said the revelations were “utterly shocking” but that the number of cases reported to authorities in Britain was rising.
“Slavery is one of those issues which people felt had been consigned to the history books. The sad reality is that it is still there,” he told BBC radio.
The anti-slavery Walk Free Foundation estimates that more than 4,000 people in Britain are trapped in debt bondage, forced marriage, human trafficking and forced labour.