Three women held captive in a London house for 30 years were beaten and brainwashed, police said Friday, as Britain struggled to comprehend its worst case of modern-day slavery.

Detectives are trying to understand the "invisible handcuffs" used to control the women, including a 30-year-old who had spent her entire life in servitude, Commander Steve Rodhouse of London's Metropolitan Police told reporters.

"What we have uncovered so far is a complicated and disturbing picture of emotional control over many years," Rodhouse said.

"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.

Also suspected of immigration offences, the pair -- who are both foreign nationals -- have been provisionally released 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.

The Guardian newspaper reported that police were investigating the possibility that the women were held as part of a cult, and that the British captive was the child of the Irish woman and the 67-year-old man.

Police declined to comment on these allegations.

Detectives do not believe the women were sexually exploited or had been the victims of human trafficking, but they told police they had been beaten.

"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 to understand what happened to them.

"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.

'They thanked us for saving their lives'

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, but only in carefully-controlled circumstances.

The case has sparked national soul-searching amid fears it is the tip of an iceberg.

Aneeta Prem, the founder of Freedom Charity which made contact with the women, 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 charity on October 18 after seeing its work on a television programme.

The charity normally deals with forced marriage and honour-based abuse.

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."

Aidan McQuade, director of Anti-Slavery International, told AFP that some victims were unable to conceive survival outside the place where they are being held.

"With those sorts of constraints in place, it's possible to allow people out, because you're essentially allowing them out on a psychological leash where you know they come back because there's nowhere else to go," he said.