A Scottish judge on Monday rejected a bid by campaigners seeking an order forcing British Prime Minister Boris Johnson to ask for a Brexit delay if he has not struck a deal with the European Union by October 19.
Lord Pentland ruled in the Court of Session there was "no doubt" that the PM accepted he had to ask for an extension in a no-deal scenario.
It would neither be "necessary nor appropriate" to force the government to ask for a Brexit delay, he added.
Lord Pentland was asked to consider the effects of the Benn Act — legislation passed by MPs with the intention of preventing the UK leaving the European Union (EU) without a deal on October 31.
It does so by requiring the prime minister to send a letter to the EU formally requesting an extension to the Brexit timetable if he fails to agree a deal by October 19.
If Johnson went back on his promise to the court 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," Lord Pentland added.
Jo Maugham QC, one of those who had sought the order, said the decision would be appealed.
Raphael Hogarth from the Institute for Government think tank said the ruling "fires a warning shot" to Johnson that he "had better not renege and destroy the 'core principles of constitutional propriety'".