LONDON (AFP) - The sister of one of the women allegedly held captive by a Maoist couple in London for 30 years was flying from Malaysia on Wednesday to meet her, as more details of the sordid case emerged.

Ms Kamar Mahtum was travelling to London hoping to confirm her long-lost sister Siti Aishah Abdul Wahab, 69, was one of three women at the centre of a case that has shocked Britain.

Ms Siti Aishah came to Britain as a high-flying student in around 1968 but turned her back on her family after joining the radical left.

The other women allegedly held by the couple are believed to be the daughter of a World War II code-breaker who also became a communist, and a 30-year-old who has spent her entire life inside the Maoist "collective".

An Indian-born man and his Tanzanian wife were arrested last week after the three women walked out of a flat in south London's edgy Brixton neighbourhood, telling police they had been trapped there for decades.

Their alleged captors, named by media as Aravindan Balakrishnan, 73, and his 67-year-old wife Chanda, have emerged as radical communists who led a small Maoist splinter group in the 1970s.

Relatives of the two older victims have described them as ordinary women who fell under the spell of the man known to activists as "Comrade Bala".

Ms Siti Aishah was reportedly so drawn in by his Marxist rhetoric that she dumped her fiance and moved in with the collective.

British media said she suffered a stroke recently but was not receiving treatment - and that this is what pushed the women to ask for help.

The second woman has been named as 59-year-old Josephine Herivel, whose father John was one of the Bletchley Park codebreakers who helped Britain and its allies win World War II.

Raised in Northern Ireland's capital Belfast, Ms Herivel is believed to have moved to London in the 1970s and, like Ms Siti Aishah, disowned her family after becoming involved with the far-left.

Appearing in court in 1978 after the police raided the Maoist group's Brixton headquarters, Ms Herivel shocked the judge by denouncing him as a "fascist lackey".

She also appears in news footage from 1997 after the mysterious death of another commune member, 44-year-old Sian Davies, who had fallen from the bathroom window of a house where Balakrishnan and his supporters were living.

When journalists went to the house to ask what had happened, Ms Herivel, a slim woman with mousy hair, refused to talk to them.

"You're part of the fascist state," she told them at the door. Two women of east Asian appearance peered out from behind her.

The third woman is thought to be Davies' daughter Rosie, who also goes by the name Prem Maopimduzi Davies. She is believed to have spent her entire life in the commune with very little contact with the outside world.

It emerged this week that she had bombarded a male neighbour with love-letters for years, begging for help but warning him not to confront her "mad and evil" captors.

"I'm like a fly trapped in a spider's web," she told neighbour Marius Feneck in one letter published by The Sun newspaper.

"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 wrote.

Several newspapers have published pictures of a slim, dark-haired woman purported to be Rosie.

Police believe the women were brainwashed and possibly beaten, but not sexually abused.

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

The women are receiving specialist care, while Mr Balakrishnan and his wife have been bailed until January pending further investigations.