A cross-party legal challenge to the UK Government on Brexit has been referred to the European Court of Justice by Scotland's highest civil court.

The group want answers on whether the withdrawal process triggered under Article 50 of the Treaty on European Union can be revoked by the UK on its own, without the consent of the other 27 EU member states.

Their challenge was rejected by the Court of Session in Edinburgh in June, but following an appeal it has now been referred to the European Court for a decision.

The Court of Session has prepared a draft request asking for a preliminary ruling from the European court under the "expedited procedure".

In his ruling Lord Carloway said: "The situation is not hypothetical or academic. Notification of withdrawal has been made.

"It may, in the absence of supervening events and perhaps in any event, take effect in about six months' time.

"The court has been asked the question of 'whether, when and how the notification... can unilaterally be revoked' in advance of the expiry of the two-year period.

"This can only be answered definitively by the Court of Justice of the EU (CJEU).

"An answer would require to be provided before this court could grant the appropriate declarator.

"In these circumstances, reference to the CJEU for a preliminary ruling under Article 267 of the TFEU is 'necessary'."

The case has been brought by a cross party group of politicians: Labour MEPs Catherine Stihler and David Martin, Joanna Cherry MP and Alyn Smith MSP of the SNP and Green MSPs Andy Wightman and Ross Greer, together with lawyer Jolyon Maugham QC, the director of the Good Law Project.

Lawyers at Balfour+Manson acted for the petitioners, with executive chairman Elaine Motion stating: "This is the most significant legal development in the Brexit process since the High Court ruled that Parliament had to legislate before the Government could invoke Article 50.

In his judgment, Lord Carloway was clear the CJEU would not be advising Parliament on "what it must or ought to do".

Instead he said it would be "merely declaring the law as part of its central function", adding that "how Parliament chooses to react to that declarator is entirely a matter for that institution".

Afterwards Mr Wightman said he was "delighted that Inner House has upheld our appeal & agreed to refer question of unilateral revocability if Article 50 to the CJEU".

A UK Government spokesman said: "We are disappointed by the decision of the court. We are giving it careful consideration.

"But as the government has repeatedly said, we are committed to implementing the result of the referendum and will not be revoking Article 50."