Shabana Mahmood’s plan to house more asylum seekers in former army barracks is facing a major hurdle after the high court ruled that a policy change forcing torture victims to share rooms was unlawful.

According to a judgment seen by the Guardian, the government failed in its duties when it forced survivors of trafficking, torture and other serious forms of violence to share rooms with strangers.

Ministers also failed to assess the impact of the changes on survivors of torture and trafficking despite the “longstanding, consistent evidence of the serious risks of harm”, Mr Justice Sweeting said on Thursday.

The ruling could have an impact on the home secretary’s plans to extend the use of shared accommodation and disused barracks to house asylum seekers. She plans to move asylum seekers out of hotels by the end of this parliament by placing many in shared housing and dormitories on Ministry of Defence land.

The charity Freedom From Torture (FFT) estimates that 10,000 survivors of torture who are housed in shared accommodation could be affected by the ruling.

Natasha Tsangarides, the associate director of advocacy at the charity, said the judgment was a “vital and resounding victory” for survivors.

“The judgment makes clear that the government acted unlawfully in changing its policy. We have seen the consequences of those changes: survivors of torture have been placed in harm’s way,” she said.

The successful legal challenge was mounted by FFT and the Helen Bamber Foundation, which work with asylum claimants who have escaped physical and mental assaults.

They said a policy introduced in February 2024 by the last government forced survivors of trafficking, torture and other serious forms of physical, psychological or sexual violence to share rooms with strangers. Prior to that date, there was a “protective presumption” that this would not happen, they said.

The present government has continued to house torture survivors in shared accommodation, they added.

The court found that the home secretary acted unlawfully by failing to consult the two charities before making fundamental changes to the policy.

The government also failed to assess the impact of the changes despite the “longstanding, consistent evidence of the serious risks of harm” faced by survivors of torture and trafficking, according to the ruling.

“These failures amount to a serious breach of [the home secretary’s] public law duties, rendering the impugned policy changes unlawful,” Sweeting said in his judgment.

The Home Office will have to decide whether to revert to the old policy, or attempt to re-introduce the changes after consulting stakeholders, implementing a formal impact assessment and obtaining expert evidence about the impact of the changes.

Kamena Dorling, a director at the Helen Bamber Foundation, said terrible living conditions had impeded the recovery of survivors of torture and trafficking.

“The decision to force more vulnerable people into large accommodation sites and shared hotel rooms was a political choice that ignored the evidence from those working with refugees every day.”

Home Office officials said about 350 people had been moved into a former barracks at Crowborough, in East Sussex, which opened to asylum seekers in January.

Plans to house another 300 asylum seekers in Cameron barracks, in Inverness, have faced delays.

A Home Office spokesperson said the department would “carefully consider” its contents. “Lessons have been learned from large sites acquired under the previous government. Strict checks are in place to maintain high health and safety standards in asylum accommodation, and those who genuinely require additional support receive it.”

The Home Office is to begin using AI facial recognition tests to estimate the age of asylum seekers claiming to be children.

The Harlow-based IT company Akhter Computers has been awarded a £322,000 contract to provide “an algorithm that can accurately predict the age of a subject”, according to an official notice published on Friday.

Unaccompanied children seeking asylum are treated differently to adults, and being under the age of 18 can sometimes affect whether asylum is granted.

When the age of an asylum seeker is disputed, immigration officers carry out assessments.

A report last year found some staff at the Western Jet Foil reception centre in Dover lacked adequate training. The report, by the independent chief inspector of borders and immigration, noted it was “inevitable” some assessments would be wrong “in the absence of a foolproof ‘test’ of chronological age”.