ONE of the UK’s most senior lawyers, the Advocate General Richard Keen QC, yesterday told the European Court of Justice in Luxembourg that the Article 50 case being brought by Scottish politicians could open a “Pandora’s box” for the European Union.

The full court of 27 judges met for four hours yesterday to hear the claim by the cross-party group of six Scottish MPs, MEPs and MSPs who want a ruling on whether the UK – effectively the Westminster Parliament – can stop the Article 50 Brexit process without the consent of the other 27 EU member states.

READ MORE: Shock poll result reveals surge in Scottish opposition to Brexit

The issue has become crucial in recent days as it has become clear that Theresa May will struggle to get her deal through the House of Commons in a fortnight’s time.

Speaking for the UK Government, Lord Keen, the former Scottish Tory chairman, said: “In Greek myth, Pandora was given a large box on her wedding, which she was warned not to open. We respectfully plead that the court should not open this box.”

Seeking a ruling that the case is inadmissible, Keen argued that it involved a “hypothetical validity challenge”. He added that the petitioners “seek to co-opt this court into their ongoing political campaign in regard to an issue of almost unparalleled political controversy and sensitivity”.

Keen stated: “If the court enters the field of parliamentary debate prematurely, then it does risk the accusation from one side or another that it is influencing the legislature or the executive in the determination of a highly charged political issue.”

Karen Banks, the Irish lawyer who is deputy director general of the Commission’s legal service, told the court that the other EU countries would have to agree to any revocation of Article 50, arguing that to allow otherwise “would leave open the possibility that that member state could use its prerogative in an abusive manner, for instance, to stop the clock on negotiations only to re-notify its intention to withdraw some time later”.

Hubert Legal, counsel for the European Council, said allowing unilateral withdrawal might mean “the main victim could be the European project altogether”.

Legal 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.”

Aidan O’Neill QC, who is representing the Scottish six, told the court that the European Council and Commission lawyers were inviting the judges to act “unconstitutionally and in contravention of the rule of law by reinterpreting the treaties.”

He said the requirement of unanimity “would curtail one of the most significant rights of a state and its peoples to decide democratically whether or not to remain in the EU” and added: “Inserting a requirement of unanimity in the European Council to make a member state’s revocation of withdrawal effective, would constitute a wholly unwanted redrafting of the treaty.

“It cannot be in the interest of the union as a whole to force a member state to leave the union against the wishes of the people. The union’s wider interest lies with member states remaining in the EU when their peoples wish to do so.”

O’Neill retorted directly to Keen’s analogy, saying that “what came out of Pandora’s box was not simply knowledge of the world’s evil, but ultimately hope, hope in and for a dangerous time”.

SNP MP Joanna Cherry QC, one of the Scottish six, told The National: “It went well. The key message is no-one is arguing that Article 50 can’t be revoked. This in itself is a victory for legal certainty.”

Judgement was reserved for a later but probably swift decision.

Cherry added: “The petitioners and interveners say it can be unilaterally revoked. The European Council and Commission say it can be revoked but only with unanimous agreement of other member states.

“The UK Govt declined to take a position either way on unilateral revocation. They simply renewed their arguments on admissibility. I don’t think that went down well.”