The Government is facing a High Court challenge over its definition of "torture" in relation to immigration detainees.
Medical Justice, a charity which helps people in detention, claims current policy is "narrow and exclusionary" and could harm vulnerable people who have suffered torture.
The charity was given the go-ahead for a judicial review against Home Secretary Sajid Javid after a hearing in London on Wednesday.
The court heard victims of torture are not usually placed in immigration detention, as they are recognised as being vulnerable and at particular risk of harm.
Detention centre doctors assess detainees and identify any potential torture victims to the Home Secretary, who will then order their release.
Ben Jaffey QC, representing Medical Justice, said the current rules came into force in July after the previous definition of torture was declared "unlawful" by a High Court judge in October last year.
He argued the definition being used at present is also unlawful, because it means a victim of torture must prove they were under the control of the perpetrator and were "powerless to resist".
Mr Jaffey told the court: "If the definition of torture is flawed, individuals who are particularly vulnerable in immigration detention will not be accurately identified, will be improperly detained and will suffer harm as a result."
Lawyers for the Home Secretary said the current definition was adopted to give effect to last year's ruling and argued it was a matter for Parliament to determine.
However, granting permission for a full hearing, Mrs Justice Moulder said Medical Justice has an "arguable case" that the current definition does not reflect the points raised in the previous High Court ruling.
She ordered that Medical Justice, a charity which relies on grants and donations, should have legal costs capped at £10,000 in the event it is not successful.
No date was given for the hearing.
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