Such a move would put First Minister Nicola Sturgeon on a constitutional collision course with Prime Minister Boris Johnson, who opposes another secession vote.

Scotland voted to remain in the U.K. by a margin of 55%-45% in a 2014 referendum that was billed as a once-in-a-generation event. A new binding referendum requires the U.K. government's approval, and Johnson insists he'll say no.

Sturgeon argues that Brexit has transformed the situation by dragging Scotland out of the European Union against its will. A narrow majority of U.K. voters opted to leave the EU in a 2016 referendum, but a large majority in Scotland voted to stay.