Police have said that three women enslaved for 30 years in a London house were beaten during their ordeal.
A 57-year-old Irish woman, a 69-year-old Malaysian and a 30-year-old British woman were rescued from a house in south London last month.
Yesterday, police arrested a man and a woman in what they said was the worst case of domestic servitude ever to emerge in Britain.
At a news conference today, Metropolitan Police Service Commander Steve Rodhouse said the women were beaten and controlled emotionally.
"What we are finding is a complicated and disturbing picture of emotional control over many years," he said.
Police also revealed that a 73-year-old man and a 67-year-old woman, who have now been released on bail, had been arrested before, in the 1970s.
No more details on those arrests were given.
Commander Rodhouse said police do not believe the case falls into the category of sexual exploitation or what is traditionally referred to as human trafficking.
"It is not as brutally obvious as women being physically restrained inside an address and not being allowed to leave," he said.
He said police are trying to understand "what were the invisible handcuffs being used to exert such a degree of control over these women".
He said that to label the investigation as domestic servitude or forced labour is "far too simplistic".
Police have said the 30-year-old woman was thought to have lived her entire life in servitude.
It remains unclear what her relationship is to the two people arrested or the two women rescued.
Commander Rodhouse said the three women had not been trafficked and that there was no link to any other groups in Britain.
The women were rescued from a house in Lambeth in October after one of them saw Aneeta Prem, founder of the Freedom Charity, on television and contacted her charity for help.
Commander Rodhouse said police are "unpicking a story that spans at least 30 years of these women's lives".
He said that to the outside world they may have appeared to have been a "normal family".
He said: "This does mean that over the course of many decades the people at the heart of this investigation, and the victims, would probably have come into contact with public services, including our own.
"That's something we need to examine fully."
He said the investigation will take "some considerable time", and there are a number of lines of inquiry to follow up, numerous statements to take and lots of exhibits to examine.
Detective Inspector Kevin Hyland, said: "Whilst we do not believe that they have been subjected to sexual abuse, we know that there has been physical abuse, described as beatings - however there is nothing to suggest that the suspects were violent towards others outside of the address.
"The two people we arrested yesterday are on bail, they have also been arrested on suspicion of immigration offences and we are working closely with the Home Office Immigration Enforcement.
"I am not prepared to disclose the nationalities of the two people arrested but they have been in this country for many years, we also do not believe the victims were trafficked into the UK.
"At this very early stage we do not believe that this investigation is linked to any other groups, and whilst it is too soon to be categoric we do not believe we are looking for other victims.
"I stress this is what we know now, and as our investigation moves on that may change.
"Last night our search of the address in south London took 12 hours, we seized 55 bags of evidence amounting to in excess of 2,500 exhibits that require examination.
"This investigation will continue for as long as is necessary and will go where the evidence takes us, what is most important to the team is that this investigation can reach the most proper and appropriate conclusion, be that ultimately a criminal prosecution."