"The suspects are of Indian and Tanzanian origin that came to the UK in the 1960s," Metropolitan Police Commander Steve Rodhouse said in a statement.
The couple, both 67 years old, were arrested on Thursday on charges of slavery and immigration offences after three women - a 69-year-old Malaysian, a 57-year-old Irish and a 30-year-old Briton - were freed by police from a house in south London.
The women were allegedly being held by the couple against their will for decades. The suspects have now been freed on bail while investigations continue.
"We believe that two of the victims met the male suspect in London through a shared political ideology, and that they lived together at an address that you could effectively call 'collective'," Rodhouse said.
"The people involved, the nature of that collective and how it operated is all subject to our investigation and we are slowly and painstakingly piecing together more information. I will not give any further information about it. Somehow that collective came to an end," he said.
Police are carrying out house to house enquiries in the Peckford Place area of Lambeth where the women were held.
The arrests were made after the Irish woman phoned a charity last month to say she was being held against her will along with two others.
The charity engaged in a series of secretive conversations with the women and contacted police. Two of the women eventually left the house, and police rescued the third.
"We received five times as many calls in 24 hours as we normally do in one week and are needing to increase our resources to cope with this extra demand.
