Andy Wightman and others asked the Court of Session to make a judgment that Article 50 can be revoked unilaterally and unconditionally by the UK Parliament.

The Court of Session has now agreed to refer this question to the European Court of Justice (ECJ), the only court that can decide this matter authoritatively and definitely, and it has asked for an expedited procedure.

The ECJ will first have to decide whether to agree to the expedited procedure, in which case it will be decided in the next two to three months.

A decision before Christmas seems realistic – right around the time the vote on the withdrawal deal is expected to be put before the UK Parliament.

A ruling in the pursuers’ favour could change things in terms of Labour’s position and that of MPs who are not convinced by either the Chequers deal or the implications of no deal.

If they know there is another option of revoking Article 50 they might just decide to do that.

The UK government argues this is an academic question as it has no intention of revoking Article 50.

Every lawyer’s opening argument is the case before the court should not be heard.

However, this is the same argument they made in the Court of Session and that court did not believe them, and also ruled the petitioners’ question was not academic or hypothetical.

It is also worth noting the Court was sitting in its highest capacity, with the Lord President writing the leading judgment, so the ruling was about as authoritative as anything you are ever likely to get out of a Scottish court.

I think the ECJ may find it difficult – although not impossible – to simply brush that off.

The UK government’s second argument will be that Article 50 can’t be revoked unilaterally, so we are stuck with it. Even if we did change our minds we would not be able to get out of this mess without the consent of the other 27 member states, or even with their consent, so there is no way out.

The UK government may also argue the ability to unilaterally withdraw Article 50 could be abused to buy more time to strike a deal, and then it could simply send another letter six months later saying it wants to leave again and reset the clock for another two years.

That would be legally problematic and might be considered an abuse of process and the law.

On the other hand, if there was a genuine change of heart, perhaps through a second referendum in which a majority of people decided to vote Remain, in that hypothetical scenario could the European Union simply turn around and say: ‘You can’t stay in any more?’

The pursuers are a diverse mix of politicians from a number of parties and parliaments, and that is something the ECJ will be aware of politically, at least, even if it does not make any difference legally.

The pursuers will argue a ruling that states members can revoke Article 50 at any time – so that Brexit is stopped with no conditions attached – would change the conversation in Britain and it is therefore relevant.

There might be a “no deal” looming in March and people might get cold feet, and if we know we can change our mind and revoke Article 50 we might do it.

If the UK can abandon Brexit before next March that would kill off the argument by people such as Guy Verhofstadt that Britain would lose its opt-outs and budget rebate if it wants to Remain.

However, if the UK actually leaves the EU and then decides to rejoin at a later date they would have to start from scratch.

The re-accession could be done fairly quickly, but I don’t think the EU will make any more allowances on the UK budget rebate or the opt-out from the euro, which would be a game changer and make it very difficult for Remainers to argue we should rejoin the EU further down the line.

The question at the heart of this is very simple in many respects – but there is no clear-cut answer at the moment because the treaties are unclear.

Most academics, I understand, think it is possible to unilaterally revoke Article 50 if there is a genuine wish to revoke it. Initially, it would be up to Donald Tusk, the President of the European Council, who would decide whether to disregard Article 50 because the letter would be addressed to him.

If he refused there might be another court case, but by that time we would be in a period of high politics so the politicians might not tolerate any further interference from the courts. The EU wants to include as many countries as possible, and they really don’t want people to leave, so I think there are a lot of legal and also psychological arguments that militate in favour of the position that Article 50 can be unilaterally revoked.

My bet would be that the European Court will rule Article 50 can be unilaterally revoked, although there is no certainty in this.

Procedurally, the ECJ would send the decision back to the Court of Session, and it would then pass judgment and it will become authoritative in UK law.

That in itself won’t change anything unless the UK government changes its mind, but those bringing the case hope it will change the parameters of the conversation.

The Prime Minister’s mantra is “Chequers or No Deal” but others say there other options such as EEA [European Economic Area] membership and a Canada-style trade deal, and we should be discussing those.

If they are then given the option of revoking Article 50 – backed by the authority of the ECJ – that will create a lot of headlines.

There has been some movement towards a People’s Vote, which I don’t think is very likely, but you could imagine a situation of total chaos, no deal, gridlock in Parliament and the requirement to have a new discussion on Brexit.

Maybe, just maybe, this judgment might contribute to the options that could be put in a People’s Vote, or in the manifestos for another general election.

Dr Tobias Lock is a senior lecturer at Edinburgh Law School, this article first appeared in The Herald