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25 October 2023

Illegal Migration Act 2023: new detention provisions come into force

5 mins

The Secretary of State for the Home Department’s powers of detention were amended on 28 September 2023, as section 12 of the Illegal Migration Act 2023 came into force.

These provisions significantly increase the Secretary of State’s powers, namely the length of time a person can be detained. The Home Office have issued new guidance ‘Detention and case progression review’ to reflect the changes.

Amending Schedule 2 of the Immigration Act 1971, the changes provide:

  • That a person can be detained for such period as, in the opinion of the Secretary of State, is reasonably necessary to enable:
    • examination or removal to be carried out;
    • for a decision to be made; or
    • for directions to be given.
  • For a person to be detained even when their examination or removal is prevented from being carried out. 
  • When detention is no longer considered necessary, the Secretary of State can continue to detain for a further period while arrangements are made for the person’s release. The length of such detention is again reliant on the SSHD’s assessment of what is reasonably necessary.

Departure from existing caselaw

These are significant departures from the previous powers to detain. 

Up to now, the limits on the Secretary of State’s power to detain were constrained by principles established in the case of R (Hardial Singh) v Governor of Durham Prison [1983] EWHC 1 (QB), as confirmed in in Lumba [2011] UKSC 12, known as the Hardial Singh principles. These are that:

(i) the Secretary of State must intend to deport the person and can only use the power to detain for that purpose;

(ii) the deportee may only be detained for a period that is reasonable in all the circumstances;

(iii) if, before the expiry of the reasonable period, it becomes apparent that the Secretary of State will not be able to effect deportation within a reasonable period, he should not seek to exercise the power of detention;

(iv) the Secretary of State should act with reasonable diligence and expedition to effect removal.

The recent changes amend the principles at (ii) and (iii) above, replacing them with this new statutory version. The guidance stresses that the previous established principle that ‘it is for the courts to decide whether there is a reasonable or sufficient prospect of a person’s removal in a reasonable timescale’ is overturned. Instead, the changes place the onus on the Secretary of State, rather than the court, to determine for how long detention is to be considered ‘reasonably necessary’.

Further, the guidance states that even where there are barriers to someone’s removal or deportation ‘for the time being, such as short-term illness, flight availability or an outstanding appeal, the new powers permit the Secretary of State to detain an individual for such a period she deems reasonably necessary. Only a longer-term barrier will be deemed more likely to be a reason why detention cannot continue to be justified.

Grace periods

Moreover, with these new powers, even when detention is no longer necessary the Secretary of State can continue to detain an individual for such period as she deems necessary while arrangements are made for the person’s release from detention, for example, whilst the Secretary of State finds appropriate bail accommodation. In practice we know that this can take weeks.

This is what has come to be called the Secretary of State’s ‘grace period’ in recent caselaw, where further detention is permitted even where continued detention in no longer reasonable. With the changes as section 12 of the Illegal Migration Act 2023, Parliament has enshrined this right in statutory legislation.


Notwithstanding the potential routes to challenge, the effect of these changes is significant and concerning, and will inevitably result in individuals experiencing longer periods in detention pending and or whilst challenging their removal or deportation.

This is particularly concerning given the damning and shocking findings on the treatments of detainees at Brook House Immigration Removal Centre as detailed in the recent release of the Brook House Inquiry Report on 19 September 2023.

Can detention still be challenged? 

In our view, there remain routes to challenge the Secretary of State’s powers to detain.

The Secretary of State’s determination of whether a period of detention is reasonable is subjective, it is her opinion, where a judge looking at whether the Secretary of State’s decision to detain is reasonable will consider on it on an objective basis, meaning they will act with impartiality. There are common and public law principles which a judge will apply to determine whether a decision is reasonable, which will act as a procedural safeguard.

As also noted in the guidance, Article 5(1)(f) of the European Convention of Human Rights (‘ECHR’) does not permit detention when there is no prospect of deportation or removal within a reasonable period and that the Secretary of State must still only detain for a purpose permitted by law. This right, and its related caselaw from the European Court of Human Rights, remains in force and can be argued where deportation or removal is not possible within a reasonable period.

As to the ‘grace period’ given to the Secretary of State to make arrangements for a person’s release, Article 5(1)(f) ECHR and Hardial Singh principle (i), which has not been overturned by these changes, only permit detention where there is an intention to deport. For those awaiting release pending the necessary arrangements being put in place, there is no longer an intention to deport that person, so continued detention – on the face of it – would appear to be unlawful and subject to challenge.

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