Trafficking victims are legally entitled to support including counselling and access to a safe house.
More than 500 potential trafficking and modern slavery victims were held in UK immigration detention centres last year, official figures suggest.
The potential victims were detained under immigration powers but were legally entitled to support including counselling and access to a safe house, according to the organisation After Exploitation.
The data mapping project obtained the figures from the Home Office through Freedom of Information requests and found 507 people who were detained at immigration removal centres during 2018 were likely to have been trafficked.
Modern slavery comes in a number of guises and can include exploitation, forced labour, domestic servitude and human trafficking.
Pierre Makhlouf, assistant director of the charity Bail for Immigration Detainees, said the figures were evidence the government "knowingly detains victims of slavery on a large scale".
Mr Makhlouf described the Home Office figures as "staggering" and said: "All too often victims of trafficking are perceived as immigration offenders rather than victims.
"As long as the agency responsible for immigration enforcement is tasked with implementing the modern slavery agenda, the government will be unable to properly implement its duty to protect victims of trafficking."
Those working with victims told MPs last week that the government's approach was to detain people for "administrative convenience".
This follows a separate report by Women for Refugee Women which slammed the Home Office for "failing" victims of modern slavery and sex trafficking.
The report has urged the government to provide victims with a year of support - up from 45 days - and to protect them from deportation or detention during that time.
It also called for anyone assessed as a victim of trafficking to be automatically released from detention.
The Home Office says it has made "significant improvements" to how it deals with victims in recent years and said 479 of the 507 people in question were assessed while in detention.
Of those, 328 were released within two days of being assessed and a total of 422 within a week.
A Home Office spokesperson said: "Any person who claims they are a victim of trafficking will, with their consent, have their claim considered by a trained specialist and will not be required to leave the country while this decision is pending.
"A positive decision entitles that person to support and guidance and is taken into consideration when deciding their immigration case."
The controversy comes as the government has pledged £10m to help build a new research base aimed at tackling modern slavery and trafficking.
The Modern Slavery Policy Centre, which is being funded by the UK Research and Innovation (UKRI) Strategic Priorities Fund, will bring together researchers, policy makers, businesses, non-governmental organisations and victims.
A study conducted last year by the Walk Free Foundation suggested there could be two slaves for every 1,000 people in the UK - meaning 136,000 victims across the country.
SOURCE: Sky News
