The trio – a 30-year-old Briton, a 57-year-old Irishwoman and a 69-year-old Malaysian – walked out of the south London property after being encouraged to act by media coverage on forced marriages.
They were said to be “deeply traumatised” following their ordeal, which police said was the most disturbing example of slavery they had encountered.
The British woman is thought to have spent her entire life in servitude.
A couple, both aged 67, were arrested at the home yesterday morning as part of the investigation into slavery and domestic servitude, Scotland Yard said.
Speaking outside Scotland Yard’s headquarters in central London, Detective Inspector Kevin Hyland said: “The human trafficking unit of the Metropolitan Police deals with many cases of servitude and forced labour.
“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.”
The investigation was launched after a call to police last month from the Freedom Charity, which helps victims of forced marriages or honour-based violence.
One of the women is understood to have contacted the charity following the ITV documentary Exposure, about forced marriages.
“Sensitive negotiations” between the charity and the women by telephone eventually led to their release on October 25.
Mr Hyland said there was a delay before the arrests were carried out as police tried to establish the facts of the case.
“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,” he said.
“We needed professional assistance from outside agencies. The last thing we wanted to do was increase that trauma.
“Until we had facts to justify where we are now, we delayed that arrest.”
He said he was unable to confirm any relationship between the suspects and the three women.
Aneeta Prem, founder of the Freedom Charity, said although the women felt they were in “massive danger”, neighbours were thought to have been oblivious to their plight.
“I don’t believe the neighbours knew anything about it at all,” she said. “It was just an ordinary house in an ordinary street. They were very restricted on everything they could do. We absolutely thrilled this has happened.”
All three women have been taken to a place of safety where they remain.
Ms Prem added: “They are going to be afforded all the help and support that can be.
“I’m so grateful they saw the news. Now they will try to re-build their lives.”
The two suspects – a man and a woman – remain in custody at a south London police station.
Frank Field MP, chairman of the modern slavery bill evidence review and vice-chairman of the human trafficking foundation, described the victims as “brave”.
He said: “People need to understand that these aren’t one- off cases – slavery is alive and well in Britain and needs to be stopped.
“We need police forces to be working much more closely with local non-government organisations, such as Freedom Charity, to help raise awareness and spot the signs of this evil, which is taking place right under our noses.
“It was incredibly brave for one of the victims to call for help – much more needs to be done to help victims come forward.”
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, she’s made clear her determination to tackle the scourge of modern slavery.”