Campaigners are expected to lodge an appeal after a judge dismissed a legal action aimed at forcing the Prime Minister to request a Brexit extension if no withdrawal deal is secured with the EU by October 19.
The Outer House of the Court of Session in Edinburgh refused the order sought by SNP MP Joanna Cherry QC and others in a judgment on Monday.
Lord Pentland ruled it was not necessary to compel Mr Johnson to comply with the terms of the so-called Benn Act given the “unequivocal assurances” of Johnson and the Government made before the court.
Ms Cherry, businessman Dale Vince, and Jolyon Maugham QC launched the legal action over fears Mr Johnson would attempt to thwart the Act passed by MPs last month.
The court’s Inner House is expected to hear an appeal on Tuesday.
Ms Cherry said: “We have forced the Tory government to concede that the Prime Minister will comply with the law, and promise to send a letter requesting a Brexit extension and not frustrate the purpose of the Benn Act.
“However, given Boris Johnson’s slippery track record of acting unlawfully, and the contradictory statements issued by the UK government – we do not trust the Tory leader or believe he can be taken at his word to obey the letter and spirit of the law.
“As such, we will appeal the decision, and expect that appeal to be heard on Tuesday.”
The Inner House is also expected to hear a request by the campaigners that Scottish judges use the unique power of “nobile officium” to empower a court official to sign the extension letter if the Prime Minister refuses to do so.
Documents submitted to the court on behalf of the Prime Minister on Friday revealed he accepted he must send the letter requesting an extension to the Brexit deadline under the terms set out in the legislation.
Mr Maugham said: “On Tuesday the Inner House will consider whether or not, if the Prime Minister refuses to do what he has told the court that he will do, the court can sign the letter for the Prime Minister, the letter mandated by the Benn Act.”