Court of Session
A resuming court hearing will rule on whether the prime minister upheld the law with his contradictory letters to the EU.
Government lawyers claimed the legal action is a “direct and manifest interference with Parliament”.
Campaigners have argued the PM cannot be trusted to obey the law.
"Absolutely not," says PM.
Downing Street source told journalists "activists choose the Scottish courts for a reason".
But a cross-party group of MPs say they will appeal the decision.
Downing Street had denied prorogation was under consideration.
More than 70 MPs are attempting to block the PM from suspending parliament before the October 31 Brexit deadline.