TWO English MPs have joined forces with a cross-party group in a legal challenge to the UK Government on Brexit in the Scottish courts.

The group believe the UK Parliament could unilaterally halt the Brexit process if the final deal negotiated by the Government is rejected by MPs at Westminster.

They are seeking a definitive ruling from the European Court of Justice (ECJ) 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.

They have to go to the Court of Session in Edinburgh first, however, to ask a judge to refer the question to the Luxembourg court, and a full hearing on the question will take place later this month.

At a procedural hearing at Scotland's highest civil court on Tuesday, Tom Brake, LibDem MP for Carshalton and Wallington, and Chris Leslie, Labour MP for Nottingham East, were accepted as "additional parties" in the case.

They are supporting the position of the group which includes Green MSPs Andy Wightman and Ross Greer, SNP MEP Alyn Smith, Labour MEPs David Martin and Catherine Stihler, SNP MP Joanna Cherry and Jo Maugham QC.

Morag Ross QC, representing Leslie and Brake, said the pair could provide a distinctive perspective on the issue as Westminster parliamentarians.

She said: "Their particular concern is as members of the Westminster parliament. They have a distinct perspective as members of that parliament who will be considering those issues in parliament."

Andrew Webster, for the UK Government, opposed accepting Brake and Leslie as additional applicants.

Aidan O'Neill QC, acting for the existing group of petitioners, said they have no objection to the additional parties joining, provided it does not hold up the timescale of proceedings.

He said: "There is an urgency in this matter in terms of the fact we are seeking a referral to the Court of Justice – there has to be expedition."

Judge Lord Boyd granted the application by the two MPs, telling the court: "I will allow Mr Brake and Mr Leslie to enter the proceedings."

He also granted the two MPs a protective expenses orders, which limits liability for legal costs.

Ross told the court it was "highly unlikely" Brake and Leslie would proceed with the case if a protective expenses order were not granted.

Earlier this year Lord Carloway, the Lord President, overturned a previous decision by another judge to halt the case's progress through the Scottish courts.

He granted permission for the substantive hearing to be held, which is now scheduled to take place on May 22.