Known as AH and IS, the men were held at the Brook House immigration centre at Gatwick Airport from December 2024 to March 2024, and from July 2023 to January 2024, respectively.
Both had described being the victims of torture before coming to the UK.
After entering the UK illegally in 2023, AH told officers after being detained that he had self-harmed in the past, heard voices and had suicidal thoughts.
He also cut himself numerous times while he was detained.
IS came to the UK legally but was given a deportation notice by the Home Office after being convicted of sexual assault in 2015.
He later successfully challenged his immigration detention at the High Court and was redetained in 2023, during which time he attempted to self-harm three times.
Both men took legal action against the Home Office at the High Court last year, with their lawyers telling a hearing last month that their detention was unlawful and that the department failed to follow rules covering the detention of adults with mental health issues.
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They also asked a judge to find that the system meant the Home Office did not comply with its duties under article three of the European Convention on Human Rights, which protects against torture and inhumane and degrading treatment.
The Home Office contested the men’s claims on the basis that mental health assessments were working as they should be.
In a judgment on Monday, Mrs Justice Jefford said there is a “clear and persistent picture of a failure of the system intended to protect” detainees from human rights abuses through mistreatment.
She also found that the various incidents of self-harm were “looked at in isolation”.
She said: “If that risk was mitigated for the time being no further action was considered necessary or appropriate.
“I entirely agree with the claimant’s case that that cannot be the intent of the policy or the proper operation of the policy and its elements.”
The judge also ruled that despite an inquiry into mistreatment at Brook House, which began in 2019, the number of reports made by GPs following assessments was too low to show the system was working well.
She said: “It is inconceivable that if the system were operating effectively, the numbers would be so low.
“The numbers have remained at this low level despite the issue, and the causes of the issue, being raised in the inquiry, in IS’s case and in the subsequent reports referred to.”
She continued: “The figures alone called for an answer but there has been no explanation for the figures other than a broad assertion that the system can be seen to be working.”
The judge added: “Nor has there been any or any satisfactory evidence that, between 2017, the period covered by the inquiry, and the period in issue in these cases, any effective steps were taken to address the failure in the system.
“The experiences of AH and IS are properly regarded as emblematic of this failure and the disconnected system and evidence that during the period with which these claims are concerned nothing had changed.”
She continued: “I will, therefore, make the declaration sought by AH and sought by IS save that the failure is in ensuring the implementation of the system and not in its design.”
Mrs Justice Jefford also said that because AH’s detention was unlawful, any use of force is common assault and he could therefore be entitled to damages.
