A dramatic legal bid to win the UK Parliament a right to revoke Article 50 which is due to be heard by the highest court in Europe is likely to succeed - raising the prospect of Brexit being halted before March next year, one of the nation’s leading experts on EU law insists.

Dr Tobias Lock, Director of European law post-graduate study at the Edinburgh Law School and author of The European Court of Justice and International Courts, said the case due to call within weeks could be decided by Christmas.

The legal action has been brought in a rare show of co-operation between Labour, Green and SNP politicians and involves MEP David Martin, MEP Catherine Stihler, MEP Alyn Smith, MP Joanna Cherry, MSP Andy Wightman and MSP Ross Greer.

Their previous attempts were rejected by government lawyers as “hypothetical and academic” and initially dismissed.

But on appeal to the Court of Session. Lords Carloway, Menzies and Drummond Young agreed it should be referred to the European Court of Justice as a matter of urgency, before Westminster votes on any Brexit deal, ahead of the current final deadline of March 29 next year.

Now Dr Tobias says it is his considered opinion, the European Court will most likely rule in their favour. That would open the door, in theory, to MPs being able to cancel Brexit and stay in the EU if no deal is reached or they are left dissatisfied with the proposed terms.

HeraldScotland:

The core of the argument is whether the UK could revoke Article 50 without requiring the assent of the other 27 EU members, and allow the UK Parliament the right to withdraw Article 50 - even if the UK Government itself still wanted to press ahead.

Writing in today’s The Herald, Dr Tobias says: “My bet would be that the European Court will rule that Article 50 can be unilaterally revoked - although there is no certainty in this.

“Procedurally the ECJ would send the decision back the Court of Session, and they would then pass judgement 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 that it will change the parameters of the conversation.”

He explained: “The pursuers will argue that a ruling which states that 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 that we can change our mind and revoke Article 50 we might do it.

“If the UK can abandon Brexit before March 2019 that would kill off the argument by people like Guy Verhofstadt [the European Parliament’s top representative on Brexit] that Britain would lose its opt-outs and budget rebate if it wants to Remain.”

Labour MEP Catherin Stihler is among those behind the action partly funded by crowdsourcing. Also writing in today’s The Herald, she said it was important the case be heard.

She said: “If we go ahead with leaving the EU next year, it will be the poorest in society who will suffer. For the sake of the workers of this country, and the generations to come, I am not prepared to sit back and accept that Brexit is inevitable.”

Equally, the SNP MP Joanna Cherry added: “Legal opinion on whether the Article 50 notification can be withdrawn by the UK without the permission of the 27 other member states is divided. “The purpose of this case is to get a definitive answer.”

Andy Wightman, Scottish Green MSP, insisted the action is necessary.

Today he writes: “The UK Government’s handling of the referendum’s aftermath and the negotiations with then EU have been inept, misguided and incoherent. The UK Parliament has a critical role to play in how this whole process ends and what shape the future takes.

“Events move fast and what seemed settled last week can be up in the air the next. It was with a view to bringing greater clarity and certainty to the process that my colleagues and I embarked on a legal case to answer a very straightforward question.

“If, for whatever reason, the UK Parliament were to wish to instruct the UK Government to revoke the Article 50 letter sent to the EU in March 2017, could it do so knowing for certain what legal effect that would have?”

David Martin, currently the longest serving MEP, added:” I welcome the Scottish Courts allowing this reference. I am confident that the European Court will say we can unilaterally with draw Article 50.

“No less an authority than Lord Kerr the author of Article 50 has opined that this is the situation.

However, we need a definitive answer to the question to avoid 11th hour incertitude.”

SNP Alyn Smyth said the day in court was necessary and hoped for a conclusion by the New Year.

HeraldScotland: Alyn Smyth is SNP MEP for Scotland

He said: “The UK Government has fought us tooth and nail, on the basis that such a revocation is hypothetical so we should just be quiet, get to the back of the bus and let them get on with it.

Well it might not be hypothetical for much longer.

“I’m not going to stand by and allow them to steer us onto the rocks, and in doing so spend most of their time trying to persuade the public the rocks are out to get us.

“We deserve a clear eyed, rational roadmap of how to exit from all this, and the European Court of Justice will give us one, before the end of the year.”

Green MSP Ross Greer previously stated: “We have to know that a no deal disaster is not the only option on the table.”

In their draft reference to the European Court, the panel of judges asked: “Where a member state has notified the European Council of its intention to withdraw from the European Union, does EU law permit that notice to be revoked unilaterally by the notifying member state?

“And, if so, subject to what conditions and with what effect relative to the member state remaining within the EU?”

Following their decision to refer the matter, the UK Government expressed “disappointment”.

It could still try to mount a counter-challenge and appeal beforehand.