Boris Johnson has ruled out giving Scotland’s first minister the authority to hold another independence referendum, paving the way for the UK Supreme Court to determine the devolved government’s legal right to a plebiscite.

In a letter to Nicola Sturgeon on Wednesday, the prime minister reiterated his government’s stance that the question had been settled in 2014 when Scots voted 55 per cent to 45 per cent to stay in the 315-year union with England.

“As our country faces unprecedented challenges at home and abroad, I cannot agree that now is a time to revisit a question, which was clearly answered by the people of Scotland in 2014,” he wrote, laying out why he would not grant her request for a so-called Section 30 order that would allow the Scottish government to legally hold such a vote.