Written constitution must include method to leave union, says SNP

SNP MP Dave Doogan (left) has urged the Prime Minister to enshrine in any constitution how countries of the UK can leave the union (Jane Barlow/PA) - (PA Archive)

A written constitution for the UK must include a method for leaving the union, the SNP has said.

The question of Scottish independence has been stymied in recent years by an argument over the process for holding a referendum, with powers to grant another vote held by Westminster and successive prime ministers refusing to engage with the topic.