The decision by judges to monitor whether Boris Johnson abides by the Benn Act and seeks a Brexit extension has been welcomed by campaigners.
The Prime Minister has been warned he faces a “sword of Damocles” over his head, should he fail to obey the law and refuse to request an extension if no deal is reached with the EU.
Judges at Edinburgh’s Court of Session delayed ruling on a legal bid aimed at forcing Mr Johnson to send a letter if no withdrawal deal is reached by October 19, with the court due to continue the case on October 21.
The Benn Act, passed by MPs in a bid to prevent a no-deal departure, obliges the Prime Minister under law to ask for an extension to Article 50 rather than leave without a deal.
The campaigners – who say Mr Johnson cannot be trusted – asked the court to use the power of “nobile officium” to allow an official to send a letter on behalf of Mr Johnson if he refuses to do so.
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.
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.
“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 decision was welcomed by SNP MP Joanna Cherry, businessman Dale Vince, and Jolyon Maugham QC – the three petitioners leading the legal challenge.
Ms Cherry said: “This decision is a victory for the petitioners and everyone who wants the Tory Government to obey the law, and call for an extension, so we can avoid a devastating no-deal Brexit.
“As a result of this vital court action, the Tory Government has been forced to concede the Prime Minister will comply with the law, and promise to send a letter requesting a Brexit extension. Crucially, he has also had to admit that he will not frustrate the purpose of the Benn Act.
“The Court’s decision is a clear signal it will keep a watch on Boris Johnson’s actions – and is holding a sword of Damocles over him in case he breaks his promise.
“The Tory Prime Minister must obey the law and call for an extension, or face the consequences – including the ability for Scotland’s Supreme Court to force a request for an extension.”
Mr Maugham said: “These cases are about keeping the Prime Minister on the straight and narrow. We have extracted from him a promise that he will comply with the law.
“If he breaks that promise, he will face the music – including possible contempt proceedings. And the courts are likely to make good any failure on his part, including signing the Benn Act letter.”
Mr Vince added: “The idea of our Prime Minister failing to uphold the law should be ridiculous, it’s an unprecedented concept – but this is where we are. Boris Johnson has repeatedly said he will not seek an extension and the UK will leave the EU on the 31st of October come what may.
“It’s for that reason we asked the courts to intervene, to prevent the very real likelihood of the law being broken and great harm ensuing to our whole country.”