Women who have survived rape and violence before coming to Britain are still routinely held in immigration detention, according to a new report.
Campaigners say female asylum seekers are being locked up despite the introduction last year of official guidance which was expected to reduce the number of vulnerable people who are detained.
A Home Office policy which took effect in September 2016 states that the "clear presumption" is that detention will not be appropriate if a person is considered to be "at risk".
People would fall into this category if they declare they are suffering from a condition, or have experienced a traumatic event such as trafficking, torture or sexual violence, that "would be likely to render them particularly vulnerable to harm if they are placed in detention or remain in detention", according to the document.
However, it also makes clear that the approach will not mean that no-one who is at risk will ever be detained.
An analysis by charity Women for Refugee Women concludes that the policy is failing to safeguard and protect vulnerable women, and has not resulted in significant change.
Researchers interviewed 26 women who had claimed asylum and had been detained after the guidelines came into force.
Of those, 22 said they were survivors of sexual or gender-based violence, including domestic violence, forced marriage and female genital mutilation.
The vast majority of the women had been detained for at least a month, while all said they were depressed during their time in detention, according to the study.
One woman from West Africa said she had been forced into prostitution in her home country.
After being helped by a friend to come to Britain, she disclosed her experience in her asylum interview but was kept in detention for six months before being released, according to the report.
"I wasn't really sleeping or eating at all, and I was having flashbacks about what had happened to me," the woman said.
"Sometimes, it felt like I was suffocating, as if the walls were closing in."
Natasha Walter, founder of Women for Refugee Women, described the research findings as "hugely disappointing".
She said: "Women who have already survived violence and abuse are still being locked up in immigration detention.
"Detention is traumatic for individual women, and it is also unnecessary, expensive and inefficient.
"We need to move away from detention and build a fair asylum process in which cases are heard and resolved while refugees are living in the community, so that they are able to start rebuilding their lives."
A Home Office spokeswoman said: "Detention is an important part of our immigration system, helping to ensure that those with no right to remain in the UK are returned to their home country if they will not leave voluntarily.
"We operate on a presumption against detention, and the adults at risk policy aims to improve our approach to identifying individuals who may be particularly vulnerable to harm in detention.
"When people are detained this is for the minimum time possible, and the dignity and welfare of those in our care is of the utmost importance."
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