Europe's highest court will decide this month whether the UK has the power to reverse Article 50, its notice of intention to leave the EU.

Downing Street had sought to block the court case through an appeal, which was rejected on Thursday.

Lawyer Jo Maugham QC, who helped to bring the case, tweeted: "The government's last-ditch effort to block our attempt to empower Parliament to act in the national interest has failed."

LONDON — Theresa May could be handed the power to unilaterally reverse Brexit after a court refused an appeal by her government to block a landmark case on the issue being referred to European courts.

In September, Edinburgh's Court of Session referred the question of whether the UK can revoke its Article 50 request to leave the EU to the European Court of Justice after a case was brought by a group of Scottish politicians.

They argued that Article 50 — which triggered the UK's EU withdrawal process — can be revoked without the agreement of the other 27 European member states.

However, the UK government sought permission to appeal the decision at the UK Supreme Court.

Lord Carloway, Scotland's most senior judge, refused the application on Thursday, meaning the case will now proceed to the ECJ as planned, with a provisional date of November 27.

The case was initially brought by a cross-party group of anti-Brexit politicians including Joanna Cherry, an SNP MP, and lawyer Jolyon Maugham QC, director of the Good Law project.

After the hearing, Maugham tweeted: "The government's last-ditch effort to block our attempt to empower Parliament to act in the national interest has failed. Application for permission to appeal refused – and the end of the line for the government."

"The government must now focus on meeting the promises made to voters in the Referendum campaign. If it cannot deliver that deal the people must be asked again – because it has no mandate to drive the country off a cliff."

'All just a bad dream'?

The court case argues that Article 50, which triggered the UK's EU withdrawal process in March 2017, can be revoked without the agreement of the other 27 European member states.

Handing May's government the unilateral power to reverse Article 50 would allow the UK to retain the perks of its current membership including the economic rebate that Margaret Thatcher negotiated in 1984 and the UK's opt-out from the Euro. These would potentially be lost were Britain forced to seek the approval of the rest of the EU to reverse Brexit.

Gunther Oettinger, the EU's Budget Commissioner has previously stated that under those circumstances "the gradual exit from the rebate would still be kept."

Jolyon Maugham told BI in October that having the power to unilaterally reverse Brexit "sweetens the option of remaining" for the UK government.

"Plainly it is better for the country if we can unilaterally revoke the Article 50 notice," Maugham added. "In that circumstance, we know that we could treat Brexit as though it was all just a bad dream."

Michel Barnier, the EU's chief Brexit negotiator, has previously said that the EU27 would need to provide their consent to reverse the Brexit process. In that scenario, should the government seek in future to remain in the EU, it could lose the perks of membership it currently enjoys.

However, it is not clear whether approval from other countries is required for a country to cancel the process because Article 50 has only been triggered once and the process has never been tested in court.

Lawyers who argued that the matter is "hypothetical" because the government does not intend revoke Article 50 were overruled by Scotland's highest judge in June, who said it was "neither academic nor premature" to ask whether it was legally competent to revoke the notice. That means has now been fast-tracked from a Scottish court to the European Court of Justice, where it is expected to be settled in as little as six weeks.

Legal opinion is split on the subject of whether the case will be successful. Those arguing against the viability of the case say handing member states the right to withdraw would undermine the integrity of the two-year notice period which defines Article 50.

However, Maugham said he believed the case still has a good prospect of succeeding.

"It's absolutely fair to say that legal opinion is divided on the matter," Maugham told Business Insider. "I genuinely don't know which way the court will jump."

A spokesperson for the Department for Exiting the Union said that it was considering the decision and added that it was "committed to implementing the result of the referendum."