Judges are expected to rule on a Brexit court case brought by campaigners who want an order forcing the Prime Minister to ask the EU for a delay if no Brexit deal is reached by October 19.
A panel of three senior judges at the Court of Session in Edinburgh will also issue a ruling on whether a court can sign this Brexit extension letter on behalf of the Government.
The requirement for the Prime Minister to request a Brexit extension if no withdrawal deal is secured with the EU by October 19 is a key provision of the so-called Benn Act, passed by MPs in a bid to prevent a no-deal departure.
Judge Lord Pentland ruled on Monday it was not necessary to compel the Prime Minister to comply with the terms of the act given “unequivocal assurances” of Boris Johnson and the Government before the court, but campaigners have lodged an appeal against this decision.
Number 10 has been accused of submitting documents to the court which contradict the Prime Minister’s public statements, such as the UK will leave the EU “do or die” on October 31.
The latest legal action – led by SNP MP Joanna Cherry, businessman Dale Vince, and Jolyon Maugham QC – seeks an order requiring the Prime Minister to send the request and another which would allow an official to do so if he does not.
This unique tool is known as “nobile officium”, but in the court hearing on Tuesday Government lawyer David Johnston QC argued the courts do not have the power to use it in these circumstances.
Aidan O’Neill QC, representing the petitioners, told the court: “What we have in this application is an application to the effect should the Government not comply with its duties, then this court, in order to preserve the rule of law, must itself authorise an individual to sign the letter and make the necessary declarations.
“It is an unprecedented step, but these are unprecedented times.”
Andrew Webster QC, also representing the Government, argued any interference from the courts could hamper the UK’s negotiations with the EU.
He claimed its position on Brexit – that it wants to leave with or without a deal on October 31 – does not mean it will not comply with the terms of the Act.
Lord Carloway questioned whether the court’s decision could be put off until after the October 19 date outlined in the act, but Mr Webster claimed this could hamper negotiations.