Former prime minister Sir John Major has suggested that Scotland could get two referendums on independence.
Sir John said a refusal from Boris Johnson to sanction another vote could increase support for separation.
“In law, the Scots require the approval of the Westminster government before they can legally hold a new independence referendum,” he said in a speech delivered at the Middle Temple’s 2020 Lecture Series.
“But refusing one might help the separatist case, by adding to the list of grievances the Scottish National Party exploit with such skill.
“The choice for the UK government is either to agree the referendum can take place – or to refuse to permit it.
“Both options come with great risk.”
Sir John, who was in Downing Street from 1990 to 1997, said the saga surrounding Britain’s exit from the European Union could offer a potential solution.
“The Westminster government could agree for an independence referendum to take place, on the basis of two referenda,” he said.
“The first to vote upon the principle of negotiations, and the second upon the outcome of them.
“The purpose of the second referendum would be that Scottish electors would know what they were voting for, and be able to compare it to what they now have.
“This did not happen with Brexit: had it done so, there may have been no Brexit.
“Many Scottish voices – and especially business – may support the logic of this: it may focus minds away from a short-term reflex opposition to a perceived English government, and back to the mutual and long-term virtues of the Union.”
Voters in Scotland opted to remain in the UK in a 2014 referendum.
But First Minister Nicola Sturgeon has argued that the 2016 vote for Brexit – which saw Scotland vote in favour of Remain – has changed things.
Recent polls have shown an increased support for independence, but Mr Johnson has so far refused to grant permission for another vote.
Kirsten Oswald, the Scottish National Party’s Westminster deputy leader, said Sir John’s comments should serve as a “wake-up call” over Mr Johnson’s “undemocratic stance”.
“Poll after poll has shown that independence is now becoming the settled will of the majority of people in Scotland, and it is for the people of Scotland to decide their future,” she said.
“It is not for out of touch Westminster governments to dictate the terms of a referendum or to dictate the future of the people of Scotland.”