The trio have had indirect contact with officers but police have had to wait until trauma experts gave them the go-ahead to take their accounts in person.
Commander Steve Rodhouse said: "We have not yet been able to formally interview the victims in this case so we don't fully understand the nature of the allegations. We are moving to a point where we will be able to interview the victims and our plan is actually to do so today.
"The victims are in the care of specialists who have got great experience of dealing with people who have been subject to trauma.
"We're working to that advice of those experts as to how best to handle those victims, to support them and of course to draw out the evidence we would need to substantiate any prosecution."
ITV News understands that one of the alleged victims is this woman, Josephine, who is now believed to be 57 years old.
She is pictured here as part of an ITV documentary in 1997 about the death of Sian Davies, who died after a fall from the window of a house used by the group.
Press reports from 1978 say a then 22-year-old commune member, Josephine Herival, was arrested during a police raid on the group's headquarters in Brixton. Sian Davies was also arrested at the same time, according to the reports.
Josephine, pictured here, is believed to be the Irish woman mentioned in recent police reports.
ITV News' UK Editor Lucy Manning understands that the couple accused of holding three women as slaves for more than 30 years are Aravindan Balakrishnan, known as Comrade Bala, and his wife Comrade Chanda.
The alleged victims - a 30-year-old Briton , a 57-year-old Irish woman and a 69-year-old Malaysian - are believed to have suffered years of "physical and mental abuse" at the hands of the couple.
The youngest of the three alleged slavery victims is said to have written letters to a neighbour, telling of her life as being "like a fly trapped in a spider's web".
The woman became infatuated with neighbour Marius Feneck, 26, the Guardian said, reportedly writing him more than 500 letters in seven years.
One letter apparently tells of how she suffered "unspeakable torment" behind locked doors and windows, and of how she was terrified that her captors - "these evil criminals... who dare to call themselves 'my relatives"' - might do something to him.
The couple accused of holding three women as slaves for more than 30 years have been linked to 13 addresses across London, The Guardian reported.
The number of properties associated with the couple, of Indian and Tanzanian origin who came to the UK in the 1960s, suggests the women may have been moved around London repeatedly over the last three decades, the paper said.