The court was asked in March to clarify the obligations on member states relating to warrants issued under the EU-UK Trade and Cooperation Agreement (TCA) by Ireland’s Supreme Court in a case involving a man sought by UK authorities for alleged terrorism offences.

The individual in the case claimed that his surrender would be incompatible with the principle that offences and penalties must be defined by law, because of an unfavourable change to the rules on release on licence adopted by the UK after the suspected commission of the offences in question.

Until the Counter-Terrorism and Sentencing Act 2021 came into force, a person in Northern Ireland who was convicted of certain terrorist offences could be granted automatic release on licence after serving half of their sentence.

Under the regime introduced by the 2021 Act, the release on licence of such a person must be approved by a specialised authority and may take place only after that person has served two-thirds of their sentence.

Ireland’s Supreme Court was satisfied that the man’s surrender was not precluded by the Constitution or the European Convention on Human Rights (ECHR), but asked the CJEU whether it was also necessary post-Brexit to consider his rights under the Charter of Fundamental Rights of the European Union.

In yesterday’s judgment, the CJEU said that member states are obliged to “ensure respect for the fundamental rights afforded by the Charter to the person who is the subject of an arrest warrant issued on the basis of the TCA” and will have to undertake an independent examination where there is a “risk of a breach of those rights”, including in the Irish case.

This examination can include “requesting additional information and guarantees from the issuing judicial authority”.

The executing judicial authority “will have to refuse to execute that arrest warrant only if… it has objective, reliable, specific and properly updated information establishing that there is a real risk of a change to the actual scope of the penalty provided for on the day on which the offence at issue was committed, involving the imposition of a heavier penalty than the one that was initially provided for,” the CJEU said.

In respect of the specific changes introduced in the UK, the court said the 2021 Act would only be incompatible with Article 49(1) of the Charter if it “retroactively alters the actual scope of the penalty provided for on the day on which the offence at issue was committed, thus entailing the imposition of a heavier penalty than the one initially provided for”.

“Although that is not, in any event, the case where that measure merely delays the eligibility threshold for release on licence, the position may be different, in particular, if that measure essentially repeals the possibility of release on licence or if it forms part of a series of measures which have the effect of increasing the intrinsic seriousness of the sentence initially provided for,” it added.

The Irish case now returns to the Supreme Court.