Scotland Yard has drawn up a new policy to ensure officers continue the deeply controversial practice of sharing data on victims of crime – including domestic and sexual violence offences – with the immigration authorities.

After a previous legal challenge from campaigners to stop the “unlawful practice” the Met ditched the policy earlier this year. Yet it has emerged that the force has redrafted the controversial measure, issuing new guidance which is almost identical to the previous policy it withdrew.

The move is now the subject of fresh legal action by Southall Black Sisters and a domestic abuse victim represented by the human rights group Liberty, in an attempt to prevent police passing on information about people suspected of being in the country illegally to deportation authorities if they come forward as victims or witnesses of crime.

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Their case argues that handing over such people to the Home Office for immigration enforcement undermines the fight against crime and erodes public safety. It also means individuals may remain in situations where they are repeatedly abused or forced to participate in crime.

One victim of violent and sexual domestic abuse, who is among those bringing the legal challenge against the Met, said that her husband had threatened to kill her, but that she had never reported him to police for fear that officers would report her to the Home Office. She was afraid that she risked being detained and potentially deported to her country of origin, where she faced persecution because her marriage had failed.

Facebook Twitter Pinterest Pragna Patel of Southall Black Sisters. Photograph: Linda Nylind/The Guardian

Aisha, not her real name, entered the UK legally and has worked for many years, but partly as a result of her husband’s abuse is currently deemed an “overstay”. She said she was “really frightened” about what might happen to her.

“I worry that he is now so angry that he might just kill me as he has threatened to do. If I was not worried about the Home Office being told about me, I would contact the police as I am so scared of him. But I am stuck now,” she said.

Following a judicial review brought by Liberty earlier this year the Met decided to drop the heavily criticised policy. Instead the force redrafted the policy in a document finalised on 11 August and called “vulnerable victims and witnesses with insecure immigration status”. It was launched three days later on 14 August.

The Met’s new policy states: “Where police are investigating a crime, and during that investigation, whether on the initial report or subsequently, it becomes apparent that the victim/witness is also suspected of being an illegal immigrant, it is wholly appropriate that the officer in the case should contact immigration enforcement.”

Debaleena Dasgupta, Liberty lawyer, said: “The Met is failing to protect victims of crime. Unless a data-sharing policy ensures all victims can seek police protection and report crimes without fear of immigration enforcement, it risks being unlawful.

“She added: We hope the Met will withdraw this policy and replace it with one that allows victims to access their protection and seek justice.”

Liberty has written to Met lawyers saying the “updated policy remains unlawful on exactly the same grounds as the previous one”.

The police must do the right thing and separate from the immigration enforcement arm of the state Pragna Patel, Southall Black Sisters

Court documents from the human rights group to the Met state: “The policy sends a clear indication to investigating police officers that they should inform HOIE [Home Office Immigration Enforcement] of a suspicion that a victim is an illegal immigrant, in other words that passing this information on is mandatory.”

Pragna Patel, director of Southall Black Sisters, said she had worked with “countless” women who “are frightened to exit from abuse and seek police protection because they fear being reported to the Home Office”. She added: “It’s time for the Met to decide who it serves – it can’t serve both the public and the Home Office at the same time since this leads to a conflict in duties and in discriminatory outcomes for abused migrant women.

“The Met Police and indeed other police forces across the UK must do the right thing and separate from the immigration enforcement arm of the state.”

A super-complaint into the sharing of data on victims with immigration enforcement authorities is currently being investigated by police watchdogs.

It is being investigated by HM Inspectorate of Constabulary, the Independent Office for Police Conduct, and the College of Policing, and could lead to recommendations including that police forces change their policies or working practices.

Dasgupta added: “In the longer term the government must implement permanent separation between all essential frontline services and immigration enforcement so everyone can access support free from fear.”