As we wait for the text of Theresa May’s letter requesting an Article 50 extension, it is worth remembering that once the UK government and the EU have agreed an extension then the UK will continue to be an EU member under international law—and international law trumps domestic law.
A Department for Exiting the European Union briefing note for ministers points out that the Vienna Convention declares:
”’A party may not invoke the provision of its internal law as justification for its failure to perform a treaty.” As a matter of EU law, it follows that in these circumstances we would remain a member state after 29 March, and the EU law consequences of that would continue to flow in the UK.’
What this means, in layman’s terms, is that even if parliament was prorogued or the statutory instrument trying to change the date was somehow defeated in parliament, the UK would still be regarded as an EU member under both EU and international law.

Britain’s best politics newsletters
You get two free articles each week when you sign up to The Spectator’s emails.
Already a subscriber? Log in
Comments
Join the debate for just £1 a month
Be part of the conversation with other Spectator readers by getting your first three months for £3.
UNLOCK ACCESS Just £1 a monthAlready a subscriber? Log in