"My preferred route to Independence is this. The Scottish Parliament should immediately legislate for a new Independence referendum. The London Government will attempt to block it. The Scottish Parliament should then convene a National Assembly of all nationally elected Scottish representatives – MSPs, MPs and MEPs. That National Assembly should declare Independence, appeal to other countries for recognition, reach agreements with the rump UK and organise a confirmatory plebiscite. That is legal, democratic and consistent with normal international practice. There will never be a better time than now for Scotland to become an Independent, normal, nation once again. It is no time for faint hearts or haverers; we must seize the moment."
https://www.craigmurray.org.uk/archives/2018/12/the-scottish-parliament-does-have-the-right-to-withdraw-from-the-act-of-union/