Judges have delayed ruling on a legal bid aimed at forcing the Prime Minister to send a letter requesting a Brexit extension if no withdrawal deal is reached by October 19.

The requirement for Boris Johnson to request an extension in such circumstances is a key provision of the so-called Benn Act, passed by MPs in a bid to prevent a no-deal departure.

Campaigners had asked the Court of Session in Edinburgh to use the unique power of “nobile officium”, which would allow an official to send a letter on behalf of Mr Johnson if he refuses to do so.

They also lodged an appeal at the court after Lord Pentland on Monday dismissed a legal action aimed at forcing Mr Johnson to request a Brexit extension if there is no deal by that date.

Three senior judges on Wednesday said that at this stage, there is no basis on which they could grant either of the campaigners’ requests and that ordinarily they would have been refused.

However they said the political debate must be played out before any decision is made, and delayed their ruling so campaigners do not have to start new proceedings if circumstances change.

They continued the case until October 21.

A lawyer acting for the petitioners said there is now a “sword of Damocles” over the Prime Minister’s head to comply with the Benn Act.

Announcing the judges’ decision, Lord Carloway, Lord President of the Court of Session, said: “Until the time for sending the letter arrives, the Prime Minister has not acted unlawfully.

Remain Supporters at a Brexit court hearing at the Court of Session in Edinburgh
Remain Supporters at a Brexit court hearing at the Court of Session in Edinburgh (Andrew Milligan/PA)

“If October 19 comes and goes without the Act having been satisfied, the petitioners would be entitled to return to court asking for the Prime Minister to have to comply with the Act.

“The situation remains fluid. What is known is that over the next two weeks circumstances will change.

“The courts understand that there is a limited amount of time. The political debate requires to be played out in the appropriate forum.”

“The court can only intervene if there is a demonstrable unlawfulness which it requires to correct. There has been no such unlawfulness.”

Judge Lord Pentland ruled on Monday it was not necessary to compel the Prime Minister to comply with the terms of the Act given the “unequivocal assurances” of Mr Johnson and the Government before the court, but campaigners 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, which have included saying the UK will leave the EU “do or die” on October 31.

Boris Johnson
The action aimed to ensure Boris Johnson adheres to the Benn Act (Aaron Chown/PA)

The latest legal action – led by SNP MP Joanna Cherry, businessman Dale Vince, and Jolyon Maugham QC – sought an order requiring the Prime Minister to send the request and another which would allow an official to do so if he does not.

Elaine Motion, a lawyer acting for the petitioners, said: “It’s an excellent judgment from the Inner House of the Court of Session, as you would expect.

“The court have indicated that there are undertakings given by the Prime Minister that he will abide by the Benn Act and not seek to frustrate it.

“In continuing the matter to the 21st, there is a sword of Damocles over the Prime Minister’s head to comply with the Benn Act, and we hope he does.

“We hope we do not have to return to court on October 21 and that politics can run its course.

“It’s only if he doesn’t comply with the orders that we have to come back to court.”