A couple who allegedly held three women as "slaves" in a London house for 30 years were prominent Maoist activists in the 1970s, according to media reports.

The couple, named by British newspapers as Indian-born Aravindan Balakrishnan and his Tanzanian wife Chanda, were arrested Thursday after their three alleged captives were freed in a police operation.

One of the victims, aged 30, is believed to have spent her entire life in servitude.

It was also reported in Britain's press on Tuesday that a female member of the sect died after falling from a bathroom window at the house in 1996.

Police are looking into the death of Sian Davies, 44, who fell two floors on Christmas Eve. She was left paralysed and died in August 1997.

A Marxist history website said Balakrishnan, 73, was a high-ranking member of the Communist Party of England (Marxist-Leninist) but had been suspended in 1974 because of the "conspiratorial and splittist activities" of his "clique".

The website also said Balakrishnan, dubbed "Comrade Bala", had been arrested in 1978 along with his wife during an attempt by police to shut down a Maoist centre in south London's Brixton area.

Police have confirmed the couple were arrested in the 1970s, but have not said why.

Police stand guard outside a block of flats in south London on November 24, 2013 where investigations have centred in a suspected slavery case.

Detectives have refused to confirm the identities of the couple, who have been bailed until January pending further investigations.

The three "slaves" -- a 57-year-old Irish woman, a Malaysian aged 69 and the 30-year-old Briton -- were freed on October 25 after one of them secretly contacted a charity.

Police said the women, who are believed to have been living in a flat in Brixton, were brainwashed and had reported being beating, but did not appear to have been sexually abused.

They were occasionally allowed out of the house and detectives are working to understand the "invisible handcuffs" that were used to control them.

Police revealed on Saturday that the two older victims had met their male captor through a "shared political ideology" and initially lived with him as part of a collective.

Meanwhile media reported that the youngest of the victims, named by The Sun newspaper as "Rosie", had bombarded a male neighbour with love letters but warned him not to confront her "mad and evil" captors.

"I'm like a fly trapped in a spider's web," she reportedly told 26-year-old Marius Feneck in one of around 500 letters sent to him over eight years.

Police stand guard outside a block of flats in south London on November 24, 2013 where investigations have centred in a suspected slavery case.

"These monsters here are mad and evil and racist -- they've locked all doors and windows and keep keys on themselves at all times," she is said to have written.

Police said Monday they were investigating 13 addresses linked to the couple, who came to Britain in the 1960s and are suspected of immigration offences as well as involvement in forced labour.

Detectives carried out house-to-house inquiries at the weekend in Brixton, one of London's poorer, more ethnically-diverse districts that was the scene of notorious anti-government riots in the 1980s.

The exact address where the women were held has not been identified, but the police operation centred on a modern, low-rise block of flats in Brixton's Peckford Place.

Specially-trained officers are now working with the women to try to understand what happened to them. All 37 officers in Scotland Yard's Human Trafficking Unit are working on the investigation.

Home Secretary Theresa May said on Sunday that tackling modern slavery in Britain was a "personal priority" and that other victims were "hidden in plain sight".