The number of potential trafficking victims who have been detained by the Home Office has tripled in four years, according to a new report.

In 2017 501 referrals for potential victims of trafficking were made among people the Home Office placed in immigration detention centres. By last year the number of referrals of potential victims who had been detained had jumped to 1,611.

The report, Abuse by the System: survivors of trafficking in immigration detention, comes from four NGOs – Helen Bamber Foundation, Medical Justice, Anti-Trafficking and Labour Exploitation Unit and Focus on Labour Exploitation – who accuse the government of deliberately putting in place a system that leads to more trafficking victims being locked up. It questions the point of officials doing this as most of those people are later released into the community.

Data shows that more than 90% of victims who claim to be trafficked have later been confirmed to be genuine through detailed investigations of their cases, via the National Referral Mechanism. In the first half of 2022 the Immigration Enforcement Competent Authority, set up by the government, made final decisions that people were indeed victims of trafficking, known as positive conclusive grounds decisions, in 97% of cases.

The government has raised the evidential bar for trafficking victims it locks up, requiring them to produce “scientific levels of evidence” that they are likely to suffer harm before they can be released from detention centres. It can be hard for trafficking survivors to obtain this level of evidence while in detention.

Fear, shame, stigmatisation and threats from traffickers can often make victims reluctant to volunteer information about their history of exploitation. But according to new trafficking rules introduced by the government, a delay in volunteering information can lead to the rejection of a trafficking claim on the grounds of “damaged credibility”.

“Survivors of trafficking are being failed and further harmed by a system that prioritises immigration control over the welfare of victims,” the report concludes.

It calls for more effective screening of trafficking victims before they are detained, independent judicial oversight of decisions to detain, and independent first responders inside detention centres to identify the most vulnerable people.

Kerry Smith, chief executive of the Helen Bamber Foundation, said: “Many of our clients have been detained by the Home Office only to be released again, their detention serving no purpose but causing them significant physical and mental harm. Immigration detention is a hugely damaging environment for survivors, leaving many feeling suicidal. We believe that a person’s recovery needs simply cannot be met in a detention setting.

“The Home Office frequently claims that people ‘abuse’ the system by claiming to be trafficked but over 90% of cases referred from detention are confirmed to be genuine victims of trafficking. There is no evidence of a process being abused – rather, people who have already been exploited and mistreated are experiencing further harm in an immigration system that is not fit for purpose.”

A Home Office spokesperson said: “The UK was the first country in the world to have dedicated laws to tackle modern slavery and we are committed to stamping out these crimes, protecting victims and bringing more perpetrators to justice. But it is clear people are abusing our rules when they have no right to be here, in order to frustrate their removal.

“Referrals to the National Referral Mechanism are often made whilst someone is in immigration detention, sometimes by serious offenders. We are making sure that criminals or those who arrive here illegally and have no right to stay are not able to hide behind laws intended to protect victims.”