It was a call to the Freedom Charity from an Irish woman that marked the beginning of the end.
The emotional woman said that her 'friend' was only ever allowed out of the home to hang washing out and occasionally walk to a shop under the tight control of one of their alleged captors.
The call last month began a painstaking operation to extricate three 'absolutely terrified' women from a house in the heart of London, where they were allegedly held for at least 30 years, in what police said could be Britain's most enduring case of domestic slavery.
One of the women, who were all described as being deeply traumatised, is believed to have been kept in the same house in the borough of Lambeth for her entire life and deprived of any 'normal' contact with the outside world since she was a baby.
It is understood that another of the victims was deprived of medical treatment despite telling her alleged captors – who were seen as heads of the family – that she believed she had suffered a stroke.
Officers from Scotland Yard's human trafficking unit staged a dawn raid yesterday on the women's home – described by charity workers as "an ordinary house on an ordinary street" – and arrested a man and a woman, both aged 67, on suspicion of slavery and forced domestic servitude.
Their alleged captives – a 30-year-old Briton, a 69-year-old Malaysian and a 57-year-old Irish woman – were released by police and staff from the London-based Freedom Charity several weeks ago.
Such are the women's fragile states, that officers have had to spend days piecing together details of their alleged ordeal before moving in to make arrests. Last night, Scotland Yard said the suspects were "not British nationals," but gave no more details.
The call that ended their apparent captivity came after the Irish woman had watched a documentary about forced marriage which focused on the Freedom Charity.
Detective Inspector Kevin Hyland, who is leading the investigation, said: "We have launched an extensive investigation (in to) these very serious allegations. All three women were deeply affected and traumatised.
"We have never seen anything of this magnitude."
The Yard said many details of the women's lives over the past three decades, including how they came to be held in the house in the first place, remained unclear because of the trauma they had suffered.
The case was immediately compared to that of Josef Fritzl, the Austrian man who kept his daughter captive for 24 years and fathered seven children with her. However, these three women are not related. Police said they were not investigating sexual abuse allegations.
Aneeta Prem, a magistrate and founder of Freedom Charity, which helps victims of forced marriage and 'honour' violence, said that after the initial call, welfare workers and police were able to identify the women's home and set up clandestine meetings.
It is believed the women suffered physical as well as mental harm. Ms Prem told Sky News: "We started in-depth talks with them when they could; it had to be pre-arranged. They gave us set times when they were able to speak to us. It was planned that they would be able to walk out of the property. "
The charity said the women had described their claimed captors as "heads of the family" and were living in a state of terror. Ms Prem said: "They felt they were in massive danger. I don't believe the neighbours knew anything about it at all. It was just an ordinary house in an ordinary street."
Police said they did not yet know if the 30-year-old had been born in the house but it was clear it had been her home ever since.