Challenging Unlawful Immigration Detention by Judicial Review

Author

Dr Bernard Andonian

Dr Bernard Andonian is a highly respected immigration, nationality and human rights lawyer, former Immigration Judge, and recognised expert known for his longstanding experience, academic achievements and contribution to landmark legal decisions.

Contact Dr Bernard Andonian View full profile

Key Points

• There is no statutory maximum time limit for UK immigration detention of adults. However, the Home Office policy requiring detention to be used for the shortest necessary period creates a framework in which prolonged or unjustified detention may be challenged as unlawful.
• The High Court in AK v Secretary of State for the Home Department [2025] EWHC 1651 (Admin) found that the Home Office’s Professional Standards Unit was operating an unlawful policy when handling detainee complaints, breaching common law principles of fairness and natural justice.
• In May 2026, the High Court granted permission for judicial review in a complex detention case on all three grounds, confirming that immigration detention decisions remain subject to full Article 5 ECHR review notwithstanding the post-Illegal Migration Act 2023 detention regime.
• Vulnerable detainees, including those with serious mental health conditions, attract heightened scrutiny, and failure to apply the Home Office’s published Adults at Risk policy provides a strong basis for judicial review.
• Remedies in a successful detention judicial review can include immediate release, damages for unlawful detention, and mandatory orders requiring the Home Office to follow its own policies.

Introduction

Immigration detention in the UK operates through an administrative, not criminal, framework. The Home Office holds individuals pending removal or the resolution of their immigration status, and unlike the criminal courts, the immigration detention system sets no maximum period for which an adult can be held. That absence of a fixed time limit, combined with rising detainee numbers in recent years, makes the courts’ role in scrutinising the lawfulness of detention decisions critically important.

The past twelve months have produced a series of significant judicial decisions confirming that immigration detention remains firmly within the scope of judicial review, that the courts will examine the process by which detention decisions are made and maintained, and that vulnerable detainees can expect a high level of scrutiny applied to the Home Office’s conduct. This article examines the current legal framework for challenging immigration detention through judicial review, the key grounds on which successful claims have been brought, and the practical steps available to those who believe their detention, or the detention of someone they know, has become unlawful.

If someone you know is detained and you believe the detention may be unlawful, our immigration detention and bail solicitors can advise on the options, including urgent bail applications and judicial review.

The Legal Framework for Immigration Detention

When Detention Is Lawful

Immigration detention is authorised under the Immigration Act 1971 and subsequent legislation. It is a power exercised by the Home Office to facilitate removal and is justified where there is a realistic prospect of removal within a reasonable timeframe and where the individual cannot be safely managed in the community through alternative means such as reporting conditions or immigration bail.

The absence of a statutory time limit does not give the Home Office a free hand. Government policy is clear that detention should be used for the shortest possible period and only where removal is imminent or where there are specific grounds to believe that the person would abscond, commit offences, or otherwise fail to comply with immigration requirements if released. In practice, cases lasting many months can and do arise, particularly where travel documents are unavailable or where legal proceedings are ongoing.

Pregnant women can only be held for up to 72 hours, which can be extended to seven days with ministerial authorisation. For other adults, the lawfulness of continued detention is assessed on an ongoing basis by reference to the Hardial Singh principles, which require that the Home Office must intend to remove the person, must be taking reasonable steps to effect removal, and must not detain for a period that is unreasonable in all the circumstances.

Article 5 ECHR and the Right to Liberty

Article 5 of the European Convention on Human Rights protects the right to liberty and security. Its application to immigration detention means that detention must be lawful under domestic law, must pursue a legitimate aim, and must not be arbitrary. The courts apply “anxious scrutiny” to Article 5 challenges, meaning a higher level of judicial examination than applies to many other administrative decisions.

The High Court’s permission decision of May 2026 confirmed that these principles survive intact under the post-Illegal Migration Act 2023 regime. Notwithstanding recent statutory amendments, detention decisions remain subject to anxious judicial scrutiny and full Article 5 ECHR review where liberty is at stake.

Recent Judicial Developments

AK v Secretary of State for the Home Department [2025] EWHC 1651 (Admin)

The High Court judgment in AK v Secretary of State for the Home Department [2025] EWHC 1651 (Admin), handed down on 1 July 2025, is a striking example of the courts’ readiness to examine the internal processes by which the Home Office handles complaints from immigration detainees.

AK brought judicial review proceedings in November 2023, arguing that the Home Office’s Professional Standards Unit (PSU) had operated an unlawful policy and practice when investigating his allegations of mistreatment. Mr Justice Sweeting found in AK’s favour. The judge held that the PSU’s approach was contrary to common law principles of fairness and natural justice, and that the Home Office was operating an unlawful policy in conducting those investigations.

The significance of the case extends beyond its specific facts. It confirms that the courts will scrutinise not only the decision to detain, but also the procedural framework within which detainees are treated while held. Failures of process, including not investigating complaints properly, can give rise to judicial review claims in their own right.

Vulnerable Detainees and the May 2026 Permission Decision

In May 2026, the High Court granted permission for judicial review in a complex immigration detention case involving a vulnerable individual with serious mental health needs. The judgment, handed down by Deputy High Court Judge Benjamin Douglas-Jones KC, addressed the treatment of mental health evidence in the detention decision-making process, the use of government redactions in judicial review proceedings, and the lawfulness of prolonged detention in light of the individual’s vulnerabilities.

The decision reinforces a line of authority requiring the Home Office to apply its Adults at Risk in Immigration Detention policy with care. Where a detainee has a serious mental health condition, the Home Office is required by that policy to take the vulnerability into account when assessing whether detention remains appropriate. Failure to do so, or failure to act on clinical evidence of deteriorating mental health, provides a strong basis for a judicial review challenge.

Separately, a case involving the proposed removal of a vulnerable individual to the United States, in which judicial review was secured in March 2026, demonstrates that serious mental health evidence can displace removal directions where the Home Office has not adequately assessed the individual’s fitness for removal and the likely impact on their clinical condition.

Grounds for Challenging Detention

The principal grounds on which immigration detention can be challenged through judicial review include:

• Unlawful policy or practice: where the Home Office has adopted a general policy or practice in managing detainees that breaches common law fairness, natural justice, or statutory obligations, as established in AK v Secretary of State for the Home Department [2025] EWHC 1651 (Admin).
• Failure to apply published policies: where the Home Office has failed to act in accordance with its own guidance, for example, by not giving effect to the Adults at Risk policy in a case involving a vulnerable detainee.
• Breach of the Hardial Singh principles: where removal is not imminent, no realistic prospect of removal exists within a reasonable time, or detention has continued for an unreasonable period in all the circumstances.
• Article 5 ECHR breach: where detention is arbitrary, disproportionate, or otherwise incompatible with the Convention right to liberty.
• Procedural unfairness: including failure to give the detainee adequate notice of the reasons for continued detention or failure to consider fresh evidence going to the lawfulness of detention.

How to Challenge Unlawful Detention

A person who believes their immigration detention is unlawful has several legal options. Immigration bail is available at any time, either from the Home Office or from the First-tier Tribunal (Immigration and Asylum Chamber), and a bail application form can be submitted by the detainee directly or with legal assistance. Where bail applications have been refused or where the basis of detention is itself challenged, judicial review is the appropriate mechanism.

The judicial review claim must be lodged within three months of the decision or event being challenged. In urgent cases, for example, where removal is imminent, it is possible to apply for an emergency injunction requiring the Home Office to halt removal while the claim is determined. Courts will grant such injunctions where there is an arguable case and where the balance of convenience favours a stay.

Before lodging a claim, the pre-action protocol requires a formal letter before claim to be sent to the Home Office, setting out the grounds and requesting a response. In detention cases where circumstances are changing rapidly, the timescales for this process can be compressed, making early specialist legal involvement essential.

Practical Guidance for Clients

In my experience, people facing detention or being detained need to:

• Seek legal advice immediately on the lawfulness of the detention, particularly if the person has been held for more than a few weeks, has a mental health condition or other vulnerability, or if removal directions have been issued.
• Request copies of the detention review records and any reports from the detention centre. Evidence of deteriorating health or inadequate review can significantly strengthen a challenge.
• Apply for immigration bail as an immediate step while the wider legal position is assessed. Release on bail does not prevent a subsequent judicial review of the original detention decision.
• Document any complaints made to the Home Office or detention centre about conditions or treatment. The AK judgment confirms that the handling of such complaints is itself subject to judicial scrutiny.
• Act within strict time limits. The three-month window for judicial review runs from the date of the unlawful decision or, where the unlawfulness is ongoing, from when the grounds of challenge first arose. Our immigration detention and bail solicitors handle urgent detention challenges and can advise on the correct approach.

Conclusion

Immigration detention, despite the absence of a statutory time limit, is not a power that can be exercised without ongoing legal justification. The courts confirmed in a series of recent decisions that the lawfulness of detention, the processes by which it is maintained, and the treatment of vulnerable detainees within the system remain fully subject to judicial review. The post-Illegal Migration Act 2023 statutory framework has not displaced Article 5 ECHR scrutiny.

For those who find themselves detained, or who are advising someone in that position, early and specialist legal engagement remains the single most effective step. The grounds for challenge are well-established, the courts have shown a clear willingness to intervene where the Home Office has fallen short, and the remedies available, including immediate release and damages, are meaningful.

Frequently Asked Questions

Is there a maximum time an adult can be held in UK immigration detention?

No, there is no statutory maximum period for adult immigration detention under the Immigration Act 1971. Government policy requires that detention be used for the shortest necessary period, and prolonged or unjustified detention can be challenged as unlawful by judicial review or by an application for immigration bail.

Can I apply for bail if I am in immigration detention?

Yes, you can apply for immigration bail at any time, either to the Home Office or to the First-tier Tribunal. The application sets out why you should be released and any conditions you are willing to accept, such as regular reporting to immigration authorities.

What is the Adults at Risk policy, and how does it protect detainees?

The Home Office publishes Adults at Risk in Immigration Detention guidance, which requires decision-makers to consider the vulnerability of detainees, including those with mental health conditions, when assessing whether continued detention is appropriate. Failure to apply this policy correctly can lead to a judicial review claim, as recent case law confirms.

Can I challenge the Home Office’s investigation into a complaint about my treatment in detention?

Yes, the High Court in AK v Secretary of State for the Home Department [2025] EWHC 1651 (Admin) confirmed that the Home Office’s handling of detainee complaints is subject to judicial review where the process breaches common law fairness and natural justice. Failure to investigate complaints properly can be challenged independently of a challenge to the underlying detention decision.

How quickly must I act if I want to challenge immigration detention?

A judicial review claim must generally be lodged within three months of the unlawful decision or event. In cases where removal directions have been issued, urgent action may be required within days or even hours. Contact our immigration judicial review solicitors as soon as possible.