EU's lawyers argue Britain cannot cancel Brexit without the bloc's consent

European Court of Justice heard arguments on Tuesday

Lawyers acting for the EU have argued that Britain should not be able to cancel Brexit without the bloc’s consent in order to prevent political chaos from engulfing the union.

The European Union’s top court is to rule on whether the UK has the power to unilaterally revoke Article 50, after legal action seeking clarity on the matter from Remain campaigners.

The UK started the legal process of leaving the EU in March 2017 by invoking the Lisbon treaty clause, which spells out the steps towards the exit door.

But the guidelines in the treaty, which run to just over 250 words, are ambiguous as to whether a country that notifies the EU it is leaving can cancel its departure and stay, even if other countries do not agree.

A legal challenge drawn up by Scottish MSPs and MEPs has asked the European Court of Justice to rule on the matter. Though a hearing took place on Tuesday, a final ruling could potentially be months away – with the clock ticking down to Britain’s departure date on 29 March 2019.

The case is expected to help clarify the options available to MPs and the government in the likely event Theresa May’s Brexit deal is rejected by parliament.

Lawyers for the campaigners argued that requiring a unanimous vote of the European Council would “ride roughshod” over EU principles that states cannot be ejected from the union against their will.

They also said parliamentarians needed to know what the options available to them were before they vote on Brexit.

British government lawyers argued that the case was inadmissible because ministers do not intend to revoke Article 50. They claimed the reactions of other member states are “unknown and unknowable” and that the campaigners simply sought “ammunition” for their political views.

The European Council’s legal team argued against unilateral revocation, stating that it would allow the UK to unfairly “keep the ball rolling” on the Article 50 period until it had a better deal from the bloc.

Lawyers acting for the European Commission meanwhile argued that states could act in an “abusive” manner by triggering and revoking Article 50 repeatedly, creating “endless uncertainty” against the spirit of the treaty.

They said that a unanimous vote should be required because extension also requires it.

Ultimately, the issue could be a moot point for Britain, as no EU state has indicated that it would block Britain’s remaining in the bloc, and Brussels chiefs such as Donald Tusk and Jean-Claude Juncker have said the UK would be welcome to stay.

Some observers however suspect the EU might try to extract concessions from the UK in the event it tried to stay.

Article 50 is clear that for a mere extension of the negotiating period, rather than a cancellation, the consent of the other member states on the European Council is required.

The UK government failed in an attempt to derail the challenge earlier this month by appealing to the UK supreme court against its referral to the ECJ.

Documents revealed in the course of that appeal however show that the government’s lawyers accept that parliament could instruct the government to revoke Article 50 – a significant point in its own right.

It has previously been determined that parliament’s consent was required for Article 50 to be triggered in the first place.

Downing Street has refused to elaborate on what it would do if Theresa May’s Brexit deal is voted down, with a spokesperson saying on Monday the prime minister had been clear there would be a period of “uncertainty”.

Jo Maugham QC, a high profile lawyer who is supporting the legal action, said: “The Article 50 case is highly significant. It could answer the question how the majority of MPs against no deal together act to prevent one. Simples – they direct the government to revoke.

“The uncomfortable truth, for paid soothsayers, is that no one knows. No one knows what happens after Theresa May’s shameful attempt to sacrifice all else at her xenophobic altar fails. Anything could happen and remaining is at least as likely as any other outcome.”