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The European Court of Justice will formally rule on whether Britain can unilaterally cancel Brexit ahead of the MPs vote on Theresa May's deal next week.
The EU's top court confirmed it will deliver its judgment at 8am UK time on Monday – with the landmark Commons vote scheduled for the next day.
Campaigners had asked the ECJ to rule on whether Article 50, which legally started the Brexit process, can be revoked by the country that triggered it. The text of the treaty clause is unclear and subject to dispute.
The ruling will come after the court's top legal advisor, the EU advocate general, recommended this week that the UK be given the power to revoke Article 50 without the consent of the EU's other member states.
If the recommendation is followed, as the advocate general's suggestions usually are, then an accidental no-deal Brexit would effectively be taken off the table, as the Government could stop it in any circumstances.
The UK Government's lawyers had argued that the case was hypothetical and should not be ruled on. The Government itself has been trying to use the threat of a no-deal to scare remain-leaning MPs into backing Theresa May's withdrawal agreement – a weapon this ruling would severely blunt.
Lawyers acting for the European Council and European Commission argued that the UK should not be able to unilaterally revoke the clause because it would allow wayward member states to cause trouble by invoking Article 50 with no intention of leaving.
But the advocate general said that as member states were sovereign countries they could still reverse commitments in international treaties before they were enacted.
The ruling on Monday will represent one of the fastest judgments ever issued by the ECJ. The process, which normally takes months or even years, has been sped up because of the time-sensitive and high-profile nature of the case.
A historic moment: thousands march to demand Final Say on BrexitShow all 65 1 /65A historic moment: thousands march to demand Final Say on Brexit A historic moment: thousands march to demand Final Say on Brexit An estimated 700,000 people marched through London to demand a final say on the withdrawal agreement
Angela Christofilou/The Independent
A historic moment: thousands march to demand Final Say on Brexit Red smoke from a canister hangs in the air as around 100,000 demonstrators march through London during a People's Vote anti-brexit demonstration savings banners and placards Anti-Brexit People's Vote March for the Future in London
Rex
A historic moment: thousands march to demand Final Say on Brexit
Angela Christofilou/The Independent
A historic moment: thousands march to demand Final Say on Brexit Mayor of London Sadiq Khan takes part in the People's Vote March for the Future in London, a march and rally in support of a second EU referendum.
PA
A historic moment: thousands march to demand Final Say on Brexit Final Say campaigners take part in the peoples vote march for the future in London 20/10/2018 Protesters wearing final Say shirts and holding placards
Angela Christofilou
A historic moment: thousands march to demand Final Say on Brexit
Angela Christofilou/The Independent
A historic moment: thousands march to demand Final Say on Brexit
Angela Christofilou/The Independent
A historic moment: thousands march to demand Final Say on Brexit
Angela Christofilou/The Independent
A historic moment: thousands march to demand Final Say on Brexit MP Chuka Umunna (left) and MP Vince Cable (right) as MP Anna Soubry (centre) addresses Anti-Brexit campaigners at a rally after the People's Vote March for the Future in London, a march and rally in support of a second EU referendum.
PA
A historic moment: thousands march to demand Final Say on Brexit
Angela Christofilou/The Independent
A historic moment: thousands march to demand Final Say on Brexit
Angela Christofilou/The Independent
A historic moment: thousands march to demand Final Say on Brexit A People’s Vote march attendee calls for a Final Say
Angela Christofilou
A historic moment: thousands march to demand Final Say on Brexit Demonstrators with banners 'We're with EU' during the People's Vote March for the Future in London, Britain, 20 October 2018. Reports state that the 'March for the Future' is to be led by a column of young people and call for a People’s Vote on the Brexit deal. After marching through central London, there will be a rally on stage in Parliament Square, including speeches from Mayor of London Sadiq Khan.
EPA
A historic moment: thousands march to demand Final Say on Brexit
Angela Christofilou/The Independent
A historic moment: thousands march to demand Final Say on Brexit
Angela Christofilou/The Independent
A historic moment: thousands march to demand Final Say on Brexit
Angela Christofilou/The Independent
A historic moment: thousands march to demand Final Say on Brexit Protesters at London’s march for the future in October
The Independent
A historic moment: thousands march to demand Final Say on Brexit Editor of The Independent Christian Broughton speaks to demonstrators in Parliament Sqaure after they take part in a march calling for a People's Vote on the final Brexit deal, in central London on October 20, 2018. - Britons dreading life outside Europe gathered from all corners of the UK to London on Saturday to try to stop their country's looming breakup with the EU.
AFP/Getty
A historic moment: thousands march to demand Final Say on Brexit A poster at the March for the Future in October
The Independent
A historic moment: thousands march to demand Final Say on Brexit Anti-Brexit campaigners take part in the People's Vote March for the Future in London, a march and rally in support of a second EU referendum.
PA
A historic moment: thousands march to demand Final Say on Brexit
Angela Christofilou/The Independent
A historic moment: thousands march to demand Final Say on Brexit Final Say campaigners take part in the peoples vote march for the future in London 20/10/2018
Angela Christofilou
A historic moment: thousands march to demand Final Say on Brexit
Angela Christofilou/The Independent
A historic moment: thousands march to demand Final Say on Brexit
Angela Christofilou/The Independent
A historic moment: thousands march to demand Final Say on Brexit Anti-Brexit campaigners take part in the People's Vote March for the Future in London, a march and rally in support of a second EU referendum.
PA
A historic moment: thousands march to demand Final Say on Brexit
Angela Christofilou/The Independent
A historic moment: thousands march to demand Final Say on Brexit
Angela Christofilou/The Independent
A historic moment: thousands march to demand Final Say on Brexit
Angela Christofilou/The Independent
A historic moment: thousands march to demand Final Say on Brexit
Angela Christofilou/The Independent
A historic moment: thousands march to demand Final Say on Brexit
Angela Christofilou/The Independent
A historic moment: thousands march to demand Final Say on Brexit
Angela Christofilou/The Independent
A historic moment: thousands march to demand Final Say on Brexit
Angela Christofilou/The Independent
A historic moment: thousands march to demand Final Say on Brexit Demonstrators hold placards as they take part in a march calling for a People's Vote on the final Brexit deal, in central London on October 20, 2018. - Britons dreading life outside Europe gathered from all corners of the UK to London on Saturday to try to stop their country's looming breakup with the EU.
AFP/Getty
A historic moment: thousands march to demand Final Say on Brexit
Angela Christofilou/The Independent
A historic moment: thousands march to demand Final Say on Brexit
Angela Christofilou/The Independent
A historic moment: thousands march to demand Final Say on Brexit
Angela Christofilou/The Independent
A historic moment: thousands march to demand Final Say on Brexit
Angela Christofilou/The Independent
A historic moment: thousands march to demand Final Say on Brexit
Angela Christofilou/The Independent
A historic moment: thousands march to demand Final Say on Brexit
Angela Christofilou
A historic moment: thousands march to demand Final Say on Brexit
Angela Christofilou/The Independent
A historic moment: thousands march to demand Final Say on Brexit
Angela Christofilou/The Independent
A historic moment: thousands march to demand Final Say on Brexit
Angela Christofilou/The Independent
A historic moment: thousands march to demand Final Say on Brexit
Angela Christofilou/The Independent
A historic moment: thousands march to demand Final Say on Brexit
Angela Christofilou/The Independent
A historic moment: thousands march to demand Final Say on Brexit
Angela Christofilou/The Independent
A historic moment: thousands march to demand Final Say on Brexit
Angela Christofilou/The Independent
A historic moment: thousands march to demand Final Say on Brexit
Angela Christofilou/The Independent
A historic moment: thousands march to demand Final Say on Brexit
Angela Christofilou/The Independent
A historic moment: thousands march to demand Final Say on Brexit
Angela Christofilou/The Independent
A historic moment: thousands march to demand Final Say on Brexit
Angela Christofilou/The Independent
A historic moment: thousands march to demand Final Say on Brexit
Angela Christofilou
A historic moment: thousands march to demand Final Say on Brexit Final Say campaigners take part in the peoples vote march for the future in London 20/10/2018 campaigner wrapped in EU flag
Angela Christofilou
A historic moment: thousands march to demand Final Say on Brexit
Angela Christofilou/The Independent
A historic moment: thousands march to demand Final Say on Brexit
Angela Christofilou/The Independent
A historic moment: thousands march to demand Final Say on Brexit Final Say campaigners take part in the peoples vote march for the future in London 20/10/2018
Angela Christofilou
A historic moment: thousands march to demand Final Say on Brexit Demonstrators pass Trafalgar Square as they take part in a march calling for a People's Vote on the final Brexit deal, in central London on October 20, 2018. - Britons dreading life outside Europe gathered from all corners of the UK to London on Saturday to try to stop their country's looming breakup with the EU.
AFP/Getty
A historic moment: thousands march to demand Final Say on Brexit Demonstrators wave Union and European flags and hold up placards as they pass Trafalgar Square, taking part in a march calling for a People's Vote on the final Brexit deal, in central London on October 20, 2018. - Britons dreading life outside Europe gathered from all corners of the UK to London on Saturday to try to stop their country's looming breakup with the EU.
AFP/Getty
A historic moment: thousands march to demand Final Say on Brexit Demonstrators hold placards as they take part in a march calling for a People's Vote on the final Brexit deal, in central London on October 20, 2018. - Britons dreading life outside Europe gathered from all corners of the UK to London on Saturday to try to stop their country's looming breakup with the EU.
AFP/Getty
A historic moment: thousands march to demand Final Say on Brexit A demonstrator holds a message during a march calling for a People's Vote on the final Brexit deal, in central London on October 20, 2018. - Britons dreading life outside Europe gathered from all corners of the UK to London on Saturday to try to stop their country's looming breakup with the EU.
AFP/Getty
A historic moment: thousands march to demand Final Say on Brexit Anti-Brexit campaigners take part in the People's Vote March for the Future in London, a march and rally in support of a second EU referendum.
PA
A historic moment: thousands march to demand Final Say on Brexit Demonstrators take part in the 'People's Vote March for the Future,' in central London, Britain, 20 October 2018. Reports state that the 'March for the Future' is to be led by a column of young people and call for a People’s Vote on the Brexit deal. After marching through central London, there will be a rally on stage in Parliament Square, including speeches from Mayor of London Sadiq Khan
EPA
A historic moment: thousands march to demand Final Say on Brexit A protester brandishes an Independent t-shirt during the Brexit March
Angela Christofilou
A historic moment: thousands march to demand Final Say on Brexit Anti-Brexit campaigners take part in the People's Vote March for the Future in London, a march and rally in support of a second EU referendum
PA
A historic moment: thousands march to demand Final Say on Brexit Tens of thousands of people take part in People's Vote March for the Future in central London. The march organised by the People's Vote campaign is led by young people calling for a People's Vote on the Brexit deal
Rex
A historic moment: thousands march to demand Final Say on Brexit Anti-Brexit campaigners take part in the People's Vote March for the Future in London, a march and rally in support of a second EU referendum
PA
On Tuesday MPs voted to put themselves in the driving seat in the PM's deal is voted down on Tuesday, amending legislation to ensure that they will get a vote on what to do next.
Government lawyers have already conceded that it is parliament rather than ministers that has the power to instruct a withdrawal of Article 50 – an assertion they made in a submission to the live case on revocation.
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