Three women have been "rescued" from a south London house as police investigate claims they were held as slaves for about 30 years.
Last month officers were contacted by Freedom Charity after it received a call from a woman saying she had been held against her will for decades.
A Malaysian woman, 69, an Irish woman, 57, and a British woman, 30, were rescued from the house on 25 October.
A man, 73, and woman, 67, were held in Lambeth and bailed until January.
The women, who are said to be "highly traumatised", were found following delicate phone conversations between the charity and the 57-year-old, who had secretly gained access to a phone.
There followed a number of phone conversations over a week, and the three woman eventually left the property when the owners of the house were not around, the charity said.
They were met by police and representatives from the group, and were then moved to a safe location.
The 30-year-old had spent her whole life in captivity. Officers are trying to establish whether she was born in the house.
Police said the relationship between the women was being investigated.
Det Insp Kevin Hyland, from the Metropolitan Police's Human Trafficking Unit, said: "We have seen some cases when people have been held for 10 years, but we have never seen anything of this magnitude before."
He added that the women had controlled lives and spent most of it indoors, but they had some freedom.
Mr Hyland said: "The women were released as soon as possible.
"There was a delay in the arrest. This was down to the fact that we had to work very carefully with these people who were highly traumatised and it was very difficult to establish the facts.
"The last thing we wanted to do was increase that trauma."
Police said the facts behind the situation were being slowly established as specialist workers were assisting the women. Officers said there was no evidence of sexual abuse.
"A television documentary on forced marriages relating to the work of Freedom Charity was the catalyst that prompted one of the victims to call for help," Mr Hyland said.
The phone call to the charity was made by the Irish woman on 18 October who said two others were being held with her.
The charity contacted the police the same day and the information was passed on to the Met Police's Human Trafficking Unit on 21 October.
Further inquiries revealed the location of the house, and after "sensitive negotiations" by the charity the women agreed to meet with police at a location on 25 October.
The Irish woman and the British woman met the police and charity workers and showed the officers where they were being held.
The 69-year-old Malaysian woman was rescued from the house and the trio were taken to a safe place.
Police said the two people arrested were not British nationals and it was "very unlikely" that the alleged victims were related to the suspects because of their nationalities.
Speaking to the BBC, Aneeta Prem, founder of Freedom Charity, said it was investigating how the women had remained hidden for so long.
"In a very busy capital city we often don't know our neighbours. We're looking at people who were kept against their will in an ordinary residential street in central London," she said.
Ms Prem said of the initial contact with the Irish woman: "She said she had been held against her will.
"She was able to use a phone but that was done in a very secret way, the people in the house didn't know she had it.
"It was a process of just over a week where there was lots of phone calls and they gained the trust of the charity, and by doing that they felt confident to reveal enough information, and obviously the police were involved, and they managed to walk out of the house when nobody was around.
"We were waiting for them with the police and we managed to get them to a place of safety.
"They have absolutely nothing now and as a charity we're trying to support them.
"It was a very emotional time, when we got the message they were outside the front door the whole call centre erupted in cheers and there were tears, and everyone was incredibly emotional to know we had helped to rescue three ladies who had been held in such horrific conditions."
Ms Prem said the two people arrested were considered the "heads of the family".
A Home Office spokesman said: "The home secretary is shocked by this appalling case and while the police need to get to the bottom of exactly what happened here, the home secretary has made clear her determination to tackle the scourge of modern slavery."
MP Frank Field, chairman of the modern slavery bill evidence review and vice-chairman of the human trafficking foundation, said: "It was incredibly brave for one of the victims to call for help - much more needs to be done to help victims come forward."