There has been much publicity about the fact that today is the last day for registering to vote in the EU referendum on 23 June.

One group who will not be entitled to register are the British ex-pats who challenged their exclusion from voting in the EU referendum. Having been unsuccessful in the High Court and the Court of Appeal, they were then refused permission to appeal by the Supreme Court on 24 May.

Section 2 of the EU Referendum Act 2015 (the 2015 Act) provides that only persons entitled to vote in a UK parliamentary election will be allowed to vote in the referendum. Two British ex-pats challenged the provision as unlawful under both EU and common law. The applicants - Mr Schindler and Ms MacLennan - remain UK citizens but have lived respectively in Italy since 1982 and Brussels since 1987. Voters can only remain on the UK electoral roll for a maximum of 15 years after leaving the country. The applicants argued that the voting restriction unlawfully infringed their right to move and reside freely within the EU.

The case raised a number of issues, including whether or not EU law was actually engaged at all, whether the provisions of s.2 are a restriction on free movement rights under EU law and, if so, whether the restriction can be justified under EU law.

On the first question, the Court of Appeal decided that EU law was not engaged at all. This might at first glance seem counter-intuitive - if the question is whether section 2 breaches EU free movement rights then EU law should be engaged.

However, Article 50(1) of the Treaty on European Union (TEU) provides that "Any Member State may decide to withdraw from the Union in accordance with its own constitutional requirements" (emphasis added). The High Court considered that this meant that the UK has a sovereign right to determine whether it wishes to withdraw from the EU treaties and that this is a matter of UK competence. The Court of Appeal agreed with this, but held that the High Court was wrong to conclude that EU lawmay still be engaged in principle insofar as the fundamental EU right to free movement was engaged. The Court of Appeal decided that the substantive rules of the Treaty (i.e. free movement rights) could not intervene to determine the constitutional requirements to be adopted by the UK under Article 50 when deciding whether to leave the EU.

The Court of Appeal went on to consider what the position would be if they were wrong about the first point and EU law were engaged. The appellants argued that the 15 year rule discouraged them from settling elsewhere and therefore restricted their free movement by requiring them to return to the UK in order to be able to vote. Like the High Court, the Court of Appeal confirmed that there was no arguable interference with free movement rights, and so rejected the case. The High Court had gone further and considered that, even if there was an interference, it could be justified under EU law as having a legitimate aim which was proportionate. The Court of Appeal declined to consider this further point, in light of the need to deal with the case urgently before the registration deadline.

The press release following the Supreme Court's decision to refuse permission made it clear that the relevant legal question is not whether the particular voting exclusion in section 2 of the 2015 Act is justifiable as a proportionate means of achieving a legitimate aim. Instead, it is (1) whether EU law applied at all (as that is a necessary condition of attacking an Act of Parliament); and (2), if so, whether there is any interference with a right of free movement.

Intriguingly, the Supreme Court side-stepped the question of whether EU law applies and decided that there was no arguable interference with the right of free movement for the reasons set out by the High Court and the Court of Appeal. The refusal of permission to appeal brought the case to an end and confirmed that the franchise will be as set out in the 2015 Act. Including anyone who makes tonight's deadline.