On 29 March 2017, the Article 50 letter was taken by two civil servants from London to Brussels on Eurostar. The cost was £985.50 including a £1.50 booking fee per person. While the letter did not get its own seat, one wonders whether anyone thought about buying it a return ticket….an Advocate General in Luxembourg has just said that the withdrawal notice may be withdrawn and, if so, presumably the letter may want to return home.

What's happened?

On 4 December 2018, in Luxembourg, Advocate General Campos Sánchez-Bordona issued his opinion to the Court of Justice of the European Union (CJEU) that the UK may withdraw its notice to withdraw from the EU. In other words, the so-called Article 50 letter could be withdrawn.

While an Advocate General's opinion is not binding on the CJEU, the vast majority of opinions are followed by the CJEU. The CJEU's summary of his opinion seem sensible and in line with conventional thinking on both public international law and European Union law. So it is likely, but not inevitable, that the CJEU will rule that the UK may withdraw its Article 50 notice where it does so in a genuine way, i.e. it does not abuse the process. Politically, it would be difficult to do otherwise. Legally, it seems sound because all the UK did was express, to use the word in Article 50, its "intention" to withdraw and there is no agreement.

Where did this opinion come from?

This case started in the Scottish Court of Session when a group of Scottish politicians asked whether the UK could withdraw its withdrawal notice. The Scottish court referred questions to the CJEU under what is known as the "preliminary reference" procedure. This is where a Member State court asks the CJEU novel questions of EU law. The CJEU answers them in the abstract and then the Member State court decides the case based on those answers. This preliminary reference was expedited by the CJEU.

The Advocate General (one of 11 Advocates General in the CJEU) believes that Article 50 of the Treaty on European Union allows the unilateral revocation of the notification of the intention to withdraw from the EU. His reasoning includes references to the Vienna Convention on the Law of Treaties which is interesting because it shows that all these "words" and "deals" do matter – they are internationally legally binding agreements governed by a legal regime.

What does this opinion mean?

Brexiteers may reject this opinion as the EU telling the UK what it may or may not do but there is welcome news in the opinion for them. The EU's approval for a change of mind by a Member State is not needed. The opinion emphasises the sovereign position of the Member State to change its mind.

The last 24 hours demonstrates the key role which "law" plays in the Brexit process and how it will unfold. In Westminster, a political storm is brewing over the publication (or not) of the legal advice given to the UK Government on the terms on which the UK would leave. In Luxembourg, the Advocate General's opinion is proving important. In Brussels, work continues to fine-tune the draft Withdrawal Agreement.

In business, it is imperative to pay attention to the legal dimension because the EU is built on law and what we are considering now are new laws and the amendment of existing ones. Business needs to know the legal implications of all of these changes because of the critical legal underpinning of the EU regime whether the UK stays or leaves.