A leading European legal official has said Britain can unilaterally cancel its withdrawal from the European Union in the face of a key parliamentary debate on Prime Minister Theresa May‘s widely criticised Brexit deal.

In a non-binding opinion issued on Tuesday, European Court of Justice (ECJ) Advocate General Campos Sanchez-Bordona said its judges can declare that a “unilateral revocation” of Article 50 – the exit clause in the bloc’s constitution – was permitted.

“That possibility continues to exist until such time as the withdrawal agreement is formally concluded,” the advice from the advocate general read.

The opinion was delivered after a group of Scottish politicians opposed to Brexit went to the ECJ to argue the United Kingdom should be able to cancel its withdrawal from the EU without the approval of the bloc’s 27 other member states.

Their case was opposed by EU institutions in a hearing last week.

A final ruling on the case is due to be made at a later date.

While Sanchez-Bordona’s opinion is not binding, the ECJ tends to follow the advocate general’s advice in the majority of its decisions.

Jo Maugham QC, a lawyer who helped crowdfund the case, said the opinion “puts the decision about our future back into the hands of our own elected representatives”.

“On this critical issue I’m sure MP’s will now search their consciences and act in the best interests of the country,” he added.

Parliament to debate Brexit deal

The UK is due to leave the EU on March 29 next year, two years after it triggered Article 50 and kick-started negotiations with European leaders over a withdrawal agreement.

Following months of tense back-and-forth talks between London and Brussels, May and EU officials announced in November they had brokered a divorce deal and declaration on future relations.

The debate over the Brexit deal, which has been widely criticised across Britain’s political spectrum, will begin in the UK parliament’s lower chamber House of Commons on Tuesday.

The debate, which is due to last for five days, will conclude with a December 11 vote in the Commons on the proposed withdrawal agreement.

Majority support would mean May can introduce a formal EU Withdrawal Agreement Bill to parliament for consideration and ratification in early 2019.

Majority opposition, however, would force the government to put forward a new plan within 21 days. In such a scenario, a renegotiation of the existing deal, general election, second referendum and no-deal Brexit could all be possible outcomes.