By Sallie George
The fate of women who have been forced into a life of sex slavery in modern Britain is often unknown.
The foundation said the women's lives became 'devoid of meaning'
The Helen Bamber Foundation, set up to help victims of torture and other human rights violations, is counselling 35 women trafficked into the UK.
Clinician Lucy Kralj said each woman had experienced "horrific brutality".
But the Home Office often did not believe what had happened to them, and some victims escaped their captors only to be jailed, the foundation said.
The government's refusal to believe the women's accounts was also reflected in the high refusal rate for asylum, it said.
Clinician Lucy Kralj said that though each woman's experience was different, all - without exception - had been subjected to "horrific levels" of physical and sexual abuse.
She said the experience of living in captivity - sometimes for years - had a profound effect on the women she had seen.
"She is violated repeatedly, daily, accompanied by physical violence and verbal insults", she said.
"She loses her sense of self, her identity. Life becomes devoid of any meaning and she can never be free of the horror through which she has lived.
"Her sense of femininity has been annihilated. She shuts her eyes and sees the horror. She looks at her body and the scars and physical pain serve as a constant reminder.
"All men are potential rapists and any hope for the future of which she once dreamed has been robbed from her.
"She finds herself repulsive and she believes that her past is transparent to everyone."
The women's experiences come at a time the UK is marking the 200th anniversary of the Parliamentary Act which led to the abolition of the slave trade.
Most of the women counselled by the foundation had been forced to "serve" upwards of 20 customers every day.
The foundation offers victims a place to regain a sense of control
Many had been beaten so badly they had sustained multiple head injuries, with several going on to develop epilepsy.
Many had become pregnant after being raped. Pregnancies were frequently terminated by traffickers but five of the women had young babies conceived while working as prostitute.
The women lived in fear that following their own escape, their family would become targeted by traffickers, while others had been rejected by their families when they had learned of their fate as a prostitute.
Ms Kralj said the aim of the foundation's work was to offer the women a place where they could begin to regain a sense of control.
Never obliged to speak of their experiences, they were offered a range of therapeutic activities and helped to get access to mainstream medical services.
But the most difficult obstacle was getting permission to stay in the country.
More than half of the women being treated by the foundation were from Albania, with others from Russia, Africa, China, Vietnam, Mongolia and India.
The majority of the women had been brought to work in London, while some had been trafficked into Birmingham and Manchester.
Most were refused asylum following interview by the Home Office, with only one granted discretionary leave to remain in the UK.
All the others had to go through an asylum protection appeal. Two were granted asylum, while another six were granted humanitarian protection for a limited period, generally of one year.
Four were refused following appeal but all had been granted a reconsideration hearing. The remaining 22 were awaiting an initial decision on their asylum application.
Ms Kralj said: "The women are frequently disbelieved by the Home Office... this is experienced by women as further devastation and proof that in the eyes of all humans her life is worthless.
"We act as witnesses to the women who have been trafficked and we are always prepared to provide evidence on their behalf to the courts and Home Office decision makers."
Jailed after escape
Sandra, from Sierra Leone, came to the UK aged 11 after being befriended by a British man who told her he could help her find a school.
Once in the UK, she was taken to a flat in London and not allowed out. When she was 12 she was drugged and gang raped.
From that day on, she was forced to serve up to 10 men every day. When she attempted suicide aged 15, Sandra was moved to a separate location and locked in solitary confinement.
Ms Kralj said: "This isolation and terror endured for a further five years with increased levels of physical violence at the hands of her pimp."
One morning, her captor forgot to lock her bedroom door before leaving the house and Sandra grabbed her chance and ran. She was later picked up by the police, who asked her for identification.
When she was unable to produce any, she was arrested and later jailed for immigration offences.
Ms Kralj said: "She is now released, her jail term over and she has been granted leave to remain in the UK for one year.
"She agreed for her story to be shared because she wants people to be aware that women being used in this way are people and not animals, although this is how they are being treated."