Downing St has made clear that the view of the European court’s senior lawyer, that Britain can unilaterally stop Brexit, “does nothing” to change the UK Government’s view that Article 50 will not be revoked.

Remain politicians across various parties welcomed the opinion of Manual Campos Sanchez-Bordona, which in the vast majority of cases is confirmed by the European Court of Justice itself; it is due to give its ruling in the next few weeks. They believe it boosts the campaign for a People’s Vote.

In a statement, the ECJ said this morning: "In answer to the question from the Scottish court, the Advocate General proposes that the Court of Justice should, in its future judgment, declare that Article 50 TEU allows the unilateral revocation of the notification of the intention to withdraw from the EU, until such time as the Withdrawal Agreement is formally concluded, provided that the revocation has been decided upon in accordance with the member state's constitutional requirements, is formally notified to the European Council and does not involve an abusive practice."

Alyn Smith, the SNP MEP one was one of those who brought the case, said: "This is a huge win for us, and a huge step forward from the highest court in the business, and confirms what we have been hoping for: that the UK can indeed change its mind on Brexit and revoke Article 50, unilaterally.

"The Advocate General Opinion is not the final judgment, but the practice of the ECJ is that the judges tend to follow the Opinion, so this is a major landmark.

"We now have a roadmap out of the Brexit shambles, a bright light has switched on above an 'Exit' sign and the false choice being offered to MPs at Westminster - that it is Mrs May's disastrous deal or chaos - is shown for what it is, an abuse of Parliament.

"There are other options, and we can stop the clock," he added.

His SNP colleague, Michael Russell, the Scottish Government’s Constitutional Relations Secretary, said: "I welcome the Advocate General's opinion and look forward to the final judgment of the Court of Justice. Rejecting a bad deal must not mean leaving with no deal.

"It is a tribute to the perseverance of the Scottish parliamentarians involved that we will finally get clarity from the Court of Justice on this important question."

Catherine Stihler, the Scottish Labour MEP, who was another member of the cross-party group involved in the legal process, said: "This is a landmark opinion from the Advocate General.

"He has made clear that the UK can stop the ticking clock of Brexit before it is too late.

"If judges accept his opinion, the UK will have the option of halting the process, and will be able to offer the chance to keep the best deal we have as a member of the EU through a People's Vote - rather than choosing between Theresa May's bad deal or a catastrophic no-deal scenario," she added.

Conservative backbencher and Remainer Dominic Grieve, the former Attorney General, also welcomed the ruling, telling BBC Radio 4's Today programme: "It's clearly significant.

"Of course, it doesn't necessarily have to be translated into a judgment, but the opinion of the advocate general is often very influential in forming the opinion of the court and it reinforces something I have to say I personally always thought was probably the case."

Asked if it made it more likely that there would be a new public vote, he said: "It is certainly helpful because it removes one of the arguments which is: 'oh well, they would never allow us to change our minds.'"

Tom Brake for the Liberal Democrats said: "We have long said that we can get out of this Brexit mess if we chose to.

"As MPs begin to debate Theresa May's terrible deal, many will be reflecting on how it compares with the deal we've currently got. UltImately, the Government must give a final say through a People's Vote with the option to remain in the EU."

Scottish peer Lord Kerr, one of the architects of Article 50, said the ECJ Advocate General’s opinion was no surprise and, if the court itself agreed, would confirm it was still up to Britain to decide whether it wanted to keep the existing deal with the EU rather than leave on the Government's terms.

"The choice facing us is not simply between the Government's deal and no deal. We can choose to change course. There is still time and, until the UK has left the EU, the Article 50 letter can be withdrawn,” he explained.

Lord Kerr added: "Despite some of the bogus claims that have been made by those who oppose staying in the EU, there would be no price to pay - political or financial - if we were to take back the Article 50 letter.

"With support growing across the country for a People's Vote, it is clear to me that this is the best way forward. The people should have the right to choose."

But No 10 was adamant the ruling was just that and was “not the final judgement” and stressed it did not alter the Government’s view that Britain would leave the EU in March next year.

"It does nothing in any event to change the clear position of the Government that Article 50 is not going to be revoked," declared Theresa May’s spokesman.

The court case was brought forward in February by a group of Scottish politicians - Labour MEPs Ms Stihler and David Martin, the SNP’s Mr Smith and his colleague Joanna Cherry, the Edinburgh MP, Green MSPs Andy Wightman and Ross Greer, as well as Jolyon Maugham QC, Director of the Good Law Project.

Mr Sanchez-Bordona’s opinion, which is not binding on the court, comes just a week after the case was heard at the ECJ following a referral from Scotland's highest civil court, the Court of Session.

Two attempts by the UK Government, which had contested the case, to appeal against the referral to the ECJ were rejected.

At the hearing last week, Aidan O'Neill QC, representing the politicians who brought the case, said they needed to know all their options on Brexit, including whether the UK could unilaterally halt the process ahead of critical votes on the Withdrawal Agreement.

Lord Keen, the Advocate General for Scotland representing the UK Government, said the case was a "hypothetical validity challenge" and those behind it seek "political ammunition to be used in, and to pressure, the UK Parliament".

Hubert Legal, representing the Council of the European Union, said allowing unilateral withdrawal could lead to "disaster", of which "the main victim could be the European project altogether".

He said Article 50 was "not ambiguous", adding: "The prerogative of acting alone will have been exhausted by putting the notification letter on the Council's table."