Appeal judges have ruled that a Scottish court has to properly examine claims that the UK should be able to unilaterally abandon Brexit without permission from other EU member states.

A panel of three judges led by Scotland’s most senior judge, Lord Carloway, the lord president, said the cross-party group of politicians behind the case had raised a point “of great importance” that had to be fully heard.

The group, which includes Labour, Scottish Green party, Scottish National party and Liberal Democrat politicians, wants the European court of justice to issue a definitive ruling on whether the UK can unilaterally withdraw its article 50 letter which triggered the Brexit process.

They say UK government ministers and the European commission are wrong to insist that the article 50 process can only be abandoned if all the other 27 EU member states agree. They argue that EU treaties make no mention of that condition.

The group, whose members include MSPs from Holyrood, Westminster MPs and two MEPs, need the permission of a Scottish court to send the case to the European court.

The appeal hearing at the court of session, Scotland’s civil court, was arranged after another judge, Lord Doherty, had thrown out the group’s initial application for an interim hearing of the case for a referral to the European court.

The appeal hearing ruled Doherty was wrong to claim the issue was hypothetical and academic since the UK government had insisted it had no intention of abandoning Brexit and so far there was no evidence parties at Westminster would block it.

Carloway said that raised significant problems for the petitioners because the statements so far by UK ministers on whether article 50 could be unilaterally withdrawn were ambiguous.

Even so, in a legal victory for the petitioners, Carloway said they were right to argue that the Westminster parliament was sovereign.

“The issue of whether it is legally possible to revoke the notice of withdrawal is one of great importance,” he said. “After all, if parliament is to be regarded as sovereign, the government’s position on the legality of revoking the notice may not be decisive.”

