Judges have put off making a decision over whether they can force Boris Johnson to delay Brexit beyond October 31.
The prime minister has repeatedly promised to take the UK out of the EU at the end of this month with or without a deal.
But under the terms of the Benn Act, Johnson must ask the EU to extend Article 50 if a deal is not agreed by October 19.
Comments by the prime minister and his chief adviser Dominic Cummings have led opposition MPs to worry the government could try to somehow bypass the legislation.
Campaigners launched a legal bid at Scotland’s highest civil court that if successful would see judges order the PM to write the letter to the EU requesting an extension to Article 50.
They also 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 Johnson if he refuses.
However, three senior judges on Wednesday said they would not make a ruling until October 21, after the October 19 deadline.
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 situation remains fluid. What is known is that over the next two weeks circumstances will change.”
He added: “The court can only intervene if there is a demonstrable unlawfulness which it requires to correct. There has been no such unlawfulness.”