An appeal is to be launched against a dismissal of legal action aimed at forcing the Prime Minister to send a letter requesting a Brexit extension.
It comes after Judge Lord Pentland announced his decision to refuse the case on Monday after considering arguments previously made at the Court of Session in Edinburgh.
He cited documents submitted to the Outer House which show Boris Johnson accepts he must send a letter to the EU requesting an extension to Article 50 under the terms of the so-called Benn Act.
The Outer House of the court ruled that the case against the Prime Minister had not been “based on reasonable apprehension of breach of statutory duty”.
Lord Pentland said: “Having regard to the Prime Minister’s and the Government’s unequivocal assurances before the court in the pleadings, in the note of argument and in oral submissions that they will comply with the 2019 Act, I am not persuaded that it is necessary for the court to grant the orders sought or any variant of them.”
But he warned that if Mr Johnson failed to comply with the legislation, it could damage the “mutual trust” between the courts and the politicians.
He stated: “I approach matters on the basis that it would be destructive of one of the core principles of constitutional propriety and of the mutual trust that is the bedrock of the relationship between the court and the Crown for the Prime Minister or the Government to renege on what they have assured the court that the Prime Minister intends to do.”
Businessman Dale Vince, SNP MP Joanna Cherry QC and Jolyon Maugham QC launched the legal action over fears Mr Johnson would attempt to thwart the Act.
The legislation requires the Prime Minister to send a letter to the EU requesting an extension if no withdrawal deal is agreed with Parliament by October 19.
They will now appeal against that decision at the court’s Inner House, which is expected to be heard on Tuesday.
Orders sought included stopping the Prime Minister from “frustrating” the will of the Act and mandating him to send the request.
Examples of possible frustration given include asking another member state to block the extension or by sending an additional letter which contradicts the original.
Speaking outside the Court of Session, Jolyon Maugham QC said: “The Court said it has promises from the Government that the Government will send the letter mandated by Parliament and will act in a way as not to frustrate Parliament’s intention in enacting the so-called Benn Act.
“For myself, I very much hope the court is right and the Government will, as it has promised to do, abide by the law.
“But there is very real doubt in my mind that the Government will act in accordance with the law and so tomorrow we will pursue our appeal against the decision of the Outer House to the Inner House of the Court of Session.”
Mr Johnson, Downing Street sources and Cabinet ministers have all repeatedly asserted the country will leave on October 31 regardless.
However, documents submitted to the court on behalf of the Prime Minister on Friday revealed he accepted he must send the letter under the terms set out in the legislation.
It also shows Number 10 accepts it cannot attempt to “frustrate” it.
Andrew Webster QC, representing the UK Government, argued this should be enough for the court to be satisfied that Mr Johnson would comply with the legislation.
He added that imposing any orders could “ruin” the negotiating strategy with the EU.
Aidan O’Neill QC, representing the petitioners, claimed Mr Johnson’s previous statements go against what he has said to the court through the documents.
He referred to promises made by the Prime Minister that he would rather be “dead in a ditch” than send a letter requesting an extension, and that the UK will leave on October 31 “do or die”.