To date, the Scottish National Party has twice asked the U.K. parliament to agree on a second referendum. Former prime minister Theresa May said no the first time.
Current Prime Minister Boris Johnson said no the second time, calling a referendum “a once in a generation event.”
Yet it’s not quite that simple (it never is when the Scots and Sassenachs are at each others’ throat.)
As Britain’s Institute for Government puts it, “Under the Scotland Act 1998, the Scottish Parliament is not allowed to pass legislation relating to matters “reserved” to Westminster, including ‘the Union of the Kingdoms of Scotland and England’. This is widely interpreted to mean that any referendum relating to Scottish independence would require Westminster approval. However, the matter has never been tested in court, so there remains some uncertainty about whether Holyrood could hold an advisory referendum without consent.”