Boris Johnson has said he will reject Nicola Sturgeon's request to stage a second referendum on independence next year if he is returned as Prime Minister.
But the Scottish First Minister hit back insisting that he will be forced to u-turn and agree to another vote if the SNP sweep to victory north of the border.
The Prime Minister insisted today that Scots were told the 2014 referendum was a "once in a generation" event and there was "no reason" to go back on this.
"I don't think people in this country think referendums are very wonderful for harmony," Mr Johnson told Sky News' Sophy Ridge on Sunday.
"We had one in 2014, the British people, the people of Scotland, were told in 2014 that that was a once-in-a-generation event."
Asked if he would grant permission for an independence referendum as prime minister, Mr Johnson stated: "No, I don't, I don't want to have one. But I don't see any reason to go back on that, on that assurance."
Ms Sturgeon has said she will request a Section 30 order seeking the power to hold a second referendum before the end of the year and told a rally of Nationalists in Glasgow on
Saturday that Scotland was at a crossroads.
And she said Mr Johnson has failed to recognise that "many thing have changed" since the last referendum in 2014, including Brexit.
"I thought it was interesting that he stopped short of saying that he would seek to block the right of the Scottish people to choose," she said of Mr Johnson's comments.
"That's not a sustainable position, it's certainly not a democratic position. Everybody in Scotland knows there's going to be another independence referendum. If the people of Scotland vote SNP, if the SNP wins this election than that sends a clear message that we want to take our future into our own hands rather than have Boris Johnson continue to impose a future upon us.
Jeremy Corbyn has indicated that he could allow a second referendum if he is Prime Minister at the "later stage" of a Labour Government.
But Ms Sturgeon insisted the timescale should be a matter for the "Scottish people and the Scottish parliament to decide."
"I've put in a very clear proposition before the Scottish people before this general election and it's an if of course, I take nothing for granted, if the SNP win that election then for any Westminster to seek to stand in the way of an independence referendum on that timescale would be seeking to ignore the democratically expressed wishes of the Scottish people.
"That is not a sustainable position, it's not a democratic position and as it happens I don't think it is a position that any Westminster politician will be able to stick to."
And the First Minister stuck to her timetable of a 2020 referendum.
"I believe it can happen next year ," she told Sophy Ridge on Sunday.
"I believe it's time for Scotland to determine what kind of future we want and what kind of country we want to be."
However, Scottish Secretary Alister Jack said the Tories were fighting to "save Scotland from the uncertainty and the division of another unwanted independence referendum".
Writing in the Scottish Mail on Sunday, he said the Conservatives were "the only party which is strong enough to stand up to Nicola Sturgeon - and stand up for the majority of people in Scotland who are sick and tired of her independence obsession".
Mr Jack stated: "We know that she will use any SNP success to demand a second referendum on leaving our United Kingdom.
"Every vote for us is a vote to say no, loud and clear, to that dreadful prospect.
"We are fighting this election not just to get Brexit sorted, but to save Scotland from the uncertainty and the division of another unwanted independence referendum.
"It is a fight we relish. We go into it with a message that could not be clearer and that we know people across Scotland want to hear."