The woman, who police said had no normal contact with the outside world, was rescued alongside a 57-year-old Irish woman and a 69-year-old from Malaysia. Their alleged captors are not British, the police confirmed, but provided no further details about their nationality.
The three "slaves" were never allowed outside unaccompanied and spent the vast majority of their lives confined to the property in Lambeth, south London, described by police as an "ordinary house in an ordinary street".
The women's ordeal finally came to an end last month when the 57-year-old contacted a charity after watching a television programme about domestic slavery.
She told charity workers that she had been held against her will in a house in Lambeth for more than 30 years.
Police were alerted and after using specially trained officers to interview the women over the telephone, two women escaped and met the authorities at an agreed location nearby on October 25. The third - the Malaysian woman - was later rescued from the house.
Yesterday, after weeks of careful investigation, police moved in and arrested two people, who were described as the "heads of the family", suggesting a criminal network would be involved. The reason for the near-month delay between rescuing the women and making the arrests was not clear.
The pair were being questioned at a south London police station, but it is not clear whether there will be further arrests in connection with the case.
Police are searching other possible linked addresses for bodies amid fears it is part of a wider abduction ring and that others may have been held but died in captivity, reports have suggested.
Detective Inspector Kevin Hyland of the Met's human trafficking unit said: "We've established that all three women were held in this situation for at least 30 years.
"Their lives were greatly controlled and for much of it they would be kept in the premises."
Hyland said police were still working to establish if the 30-year-old woman had been born in the house but he said the indications were that she had spent her entire life there.
Asked if she had ever attended school, he said: "The 30-year-old had no contact with the outside world that one would see as normal."
Hyland went on: "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.
"It's part of our investigation - who had any freedom, what sort of freedom, under what conditions that freedom was allowed."
Police are investigating the possibility that the victims may have been related in some way, but given their different nationalities that seems unlikely.
Police have also said there have been no allegations of sexual abuse made by the victims.
Freedom, a charity which offers advice and support to victims of forced marriages, contacted police after one of the women got in touch last month.
Aneeta Prem, the founder of the charity, said the alleged victims were extremely vulnerable, but had been able to walk out of the house on their own where they were met by police.
"I think it's a real rarity, I certainly haven't heard of anything like this before. I've heard of stories abroad but not in the centre of London."
The case has led to inevitable comparisons to that of Josef Fritzl, the Austrian who kept his daughter confined to the cellar of his home for 24 years.
In May this year three women were freed from a house in Cleveland, Ohio, after being kidnapped and held against their will for more than a decade.
The Home Secretary, Theresa May, expressed her shock at the case.
A 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."
Metropolitan Police Commissioner Sir Bernard Hogan-Howe said: "If the allegations are true that someone's been kept against their will or been abused for 30 years that's a horrendous thing and we're all shocked by that."
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 - modern 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," said Field.
"It was incredibly brave for one of the victims to call for help - much more needs to be done to help victims come forward."
The Forced Marriage Unit - a joint operation by the Home Office and the Foreign and Commonwealth Office - earlier revealed it helped in 1485 cases of possible forced marriage last year, involving 60 countries across Europe, Asia, the Middle East, Africa and North America.
The statistics for last year show that of the 744 cases where the age was known, more than 600 involved people under the age of 26.
