Victims of torture are being held in detention while their asylum claims are assessed due to an unsuitable screening process, inspectors have claimed.
The system used by the troubled UK Border Agency (UKBA) was not tailored to determine whether an asylum seeker was suitable for the detained fast-track (DFT) scheme, a review found.
John Vine, the independent Chief Inspector of the UK Border Agency (UKBA), said there was "a particular risk that the victims of torture or trafficking could be allocated to the DFT contrary to the agency's own policy".
The scheme, first brought in eight years ago when asylum applications were at record levels, is used when officials deem that an individual's circumstances are uncomplicated and a decision can be made quickly while they are held in detention.
But Mr Vine said "a significant number of people initially screened as suitable for the DFT were subsequently released".
A review of 114 cases found 30% were taken out of detention at some stage and 27% of these were released before a decision on their asylum claim had been made.
Almost half of these (44%) were released due to health issues and evidence they were victims of torture or trafficking while almost a third (32%) were released because of difficulties in obtaining travel documentation for removal.
Mr Vine said: "While safeguards were in place once people had been detained, there remained a particular risk that the victims of torture or trafficking could be allocated to the DFT contrary to the agency's own policy."
Keith Best, chief executive of Freedom from Torture, said: "Survivors of torture keep being wrongly allocated to the detained fast-track.
"We agree that improving the privacy of screening will help some survivors to share their horrific experiences with officials.
"That said, no amount of tinkering with the format of screening will get around the fact that UKBA cannot seek details of the asylum claim at this early stage because applicants have not yet had access to legal advice."
He added that the report's findings, "if followed through to their logical conclusion, have a far stronger implication - that the DFT is flawed by design and has no place in a fair asylum system."
Dr Juliet Cohen, the group's head of doctors, added: "When a person has been tortured by uniformed figures in a detention setting, further detention is likely to be traumatising and inhibit their ability to give a detailed account of everything they have suffered.
"This is exactly why UKBA policy is not to process torture survivors through DFT. However in reality a number of extremely vulnerable people are still regularly routed in."
Donna Covey, chief executive of the Refugee Council, said: "It is unacceptable that victims of torture or trafficking are being allocated to the DFT because of a hurried and completely unsuitable screening process.
"Instead of focusing on meeting set timescales and celebrating high removal rates, we urge the Government to review whether the DFT can really be part of a fair, effective asylum system.
"In the meantime, they must stop detaining people in the fast-track process unless they can guarantee no victims of trafficking or torture will be part of this."
The report also found that more than a third (38%) of asylum seekers detained while their claims are being assessed are held for longer than three months before being removed.
On average, decisions alone were taking 13 days to be made, despite the agency's stated target of just three to four days.
These delays in interviewing the asylum seekers led to more than £100,000 in extra costs in the sample cases alone.
Mr Vine, whose reviews of the UKBA's work has led to Home Secretary Theresa May splitting off the work of the Border Force into a separate agency from next month, added that in the cases sampled, only one person was granted asylum and 98 were refused.
Overall, less than three quarters (73%) of people whose claims were refused and who had no right to remain in the UK were removed, despite the appeals process upholding 93% of the UKBA's decisions.
But Jerome Phelps, director of Detention Action, said the scheme was "outdated, unfair and expensive".
"The Government policy of routinely depriving people of their liberty for weeks and months simply for claiming asylum, for the Government's administrative convenience, is one that must be abolished," he said.
A UKBA spokesman said: "The DFT system plays a fundamental role in making sure asylum claims can be processed and decided as swiftly as possible.
"This helps those who are granted asylum quickly build lives within the country, while ensuring we can remove people who have no right to remain in the UK.
"Around three quarters of people whose claims were refused were removed from the UK. Of those, almost two thirds were removed within three months.
"However, we are allocating more staff to help speed up the processing of these cases."