The victims were identified as a 69-year-old Malaysian, a 57-year-old Irish and a 30-year-old British, Xinhua reported Thursday citing media reports.
The 67-year-old couple who held them slaves were arrested from their house in Lambeth.
A non-governmental organisation received a call in October from a woman stating that she was held against her will at a house in London for more than 30 years, who in turn informed the police, reported The Guardian.
"All three women, who were highly traumatized, were taken to a place of safety," said police.
The victims were not related and police found no evidence of sexual abuse, according to a media report.
Police are trying to find out whether the youngest victim was born in the house or was taken as a baby, as she had been in servitude for her entire life without any contact from the outside world.
"We have seen some cases when people have been held for 10 years, but we have never seen anything of this magnitude before," said an officer.
BBC described the women as having "controlled lives" and spent most of them indoors.
The Home Office is shocked at the case, and declared its determination to root out modern slavery.