Scotland Yard has revealed that two of the three women, whose rescue was revealed on Thursday, had lived in a “collective” with a man who was arrested after meeting through a “shared political ideology”.
The man and a woman, both 67, have been released on bail after being arrested in connection with the investigation into slavery and domestic servitude.
Ms May said the “one positive” of the case was that more people were aware of the issue of slavery which still has “shocking presence in modern Britain”.
“It is all around us, hidden in plain sight,” she said.
“It is walking our streets, supplying shops and supermarkets, working in fields, factories or nail bars, trapped in brothels or cowering behind the curtains in an ordinary street: slavery.
“Something most of us thought consigned to history books, belonging to a different century, is a shameful and shocking presence in modern Britain.”
She said the facts behind the Lambeth, south London case were still not known and the investigation “must be allowed to take its course”.
“Whatever the outcome, the one positive is that it has raised awareness of the issue of slavery in the public and media mind,” she said.
Officers were conducting house-to-house inquiries yesterday in Peckford Place, Brixton, where the three women were found.
The couple bailed to a date in January are of Indian and Tanzanian origin and came to the UK in the 1960s, police said.
All three of the alleged victims — a 57-year-old Irish woman, a 30-year-old British woman, and a 69-year-old Malaysian woman — were believed to have suffered “emotional and physical abuse”, said Metropolitan police commander Steve Rodhouse.
The Met said that part of the agreement on Oct 25 when the women were removed from the address was that police would not take any action at that stage. None of the women were reported missing, police said. Officers have recovered a birth certificate for the 30-year-old woman, who is believed to have lived her entire life in servitude, but no other official documents for her have been found.
The case came to light after the Irish woman rang the Freedom Charity last month to say she had been held against her will. All three women are now in the care of a specialist non-governmental organisation,.
It emerged on Friday that the couple on bail were previously arrested in the 1970s, although police have not said why they were detained.
Meanwhile, the MP in charge of reviewing evidence of slavery in Britain said the case was the “tip of a rather large iceberg”.
Frank Field, chair of the Modern Slavery Bill evidence review, said criminal gangs were making “huge sums of money” from people being imported into the UK to work “almost for nothing”.
He said many victims who escape have no way of communicating because they speak little or no English and often come from countries where they are “deeply suspicious” of the police.
“We’ve had this example of domestic slavery but people are being imported to work, almost for nothing, in industry,” he said.
Mr Field said it appeared the issue of slavery was getting worse as authorities were becoming more successful with prosecutions.
“I would have thought it’s safe to act on the assumption that the examples we’ve had in the last few months are the tip of a rather large iceberg.”