Police will formally interview three women allegedly held as slaves for the first time today.
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."
One of the three 'slavery victims' is reportedly the daughter of a Second World War codebreaker, The Times (£) claims.
Josephine Herivel, in her fifties, is believed to be the daughter of John - a leading codebreaker at Bletchley Park who helped decipher the Enigma code.
She joined slavery suspect Aravindan Balakrishnan's extremist collective in the 1970s after moving to London to study, turning her back on her family.
When her father died in 2011 obituaries only made mention of two daughters, Mary and Susan, who now live in London.
Family friend Frances Presley told the newspaper: "They have tried to contact her for years. I know she was involved in some kind of cult group. My understanding is that she cut herself off [from the family]. I know they have always tried their best."
Aravindan and Chanda Balakrishnan were arrested on suspicion of slavery related offences amid claims that three women were held against their will for more than 30 years.
ITV News has uncovered the first pictures of the man arrested over allegations of keeping three women as slaves in a house in south London.
Aravindan Balakrishnan, known as Comrade Bala, is understood to be the leader of a 1970s Maoist commune.
He was featured, along with his alleged victims, in a documentary in 1997 into the death of a woman called Sian Davies who died at the group's house in Brixton.
It emerged today that one of the victims may be the daughter of Sian Davies. UK Editor Lucy Manning reports.
Documentary footage obtained by ITV News also shows Comrade Chanda, the wife of Aravindan Balakrishnan, outside a 1997 inquest into the death of commune member Sian Davies.
Chanda, pictured in a wheelchair and to the left of the man known as Comrade Bala, was arrested with her husband last week as part of an investigation into slavery and domestic servitude.
In another clip from a 1997 ITV documentary, Aravindan Balakrishnan, also known as Comrade Bala, is seen walking towards an inquest wearing a pink shirt and brown jacket.
Balakrishnan is the man arrested as part of the so-called slavery investigation in south London.
ITV News believes this woman to be Aishah, the 69-year-old Malaysian woman rescued from the alleged 'slavery' house in south London.
She is pictured in a 1997 documentary about the death of Sian Davies, who died following a fall from a window of a house used by the group.
According the press reports from 1978, a 34-year-old woman called Aishe Waham was arrested following a police raid on the group's headquarters.
Press reports from 1997 quote an Aisha Wahab giving evidence at a coroners' inquest into Sian Davies' death.
A Telegraph report today says the woman was originally known as Aishah Mautum, who moved to Britain in 1968 from Malaysia before becoming involved with the Maoist group.
ITV News has uncovered documentary footage of members of the alleged 'slavery' commune in south London.
These pictures from 1997 show members of the group responding to questions about the death of group member Sian Davies, who died following a fall from a window of a house used by the group.
Members are also seen attending an inquest into the death of Sian Davies, who was paralysed following the fall.
Miss Davies' family criticised the group at the inquest and in an interview today for not telling them for several months that she was paralysed in hospital.
The family only learned of the fall when Miss Davies died in hospital.
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 has obtained the first pictures of Comrade Bala, the man arrested as part of the so-called slavery investigation in south London.
In this footage the man, whose real name is Aravindan Balakrishnan, is seen wearing a brown jacket and blue trousers as he attends the inquest into the death of commune member Sian Davies in 1997.