Boris Johnson has ruled out granting permission for a second Scottish independence vote while he is Prime Minister – despite Nicola Sturgeon insisting “things have changed” since the country voted to stay part of the UK five years ago.

Mr Johnson insisted there was no reason to go back on assurances given by SNP leaders in 2014 that the referendum then was a “once-in-a-generation” event.

He made the comments after the Scottish First Minister revealed she is to request the power to hold a legally-binding independence referendum within days of the December 12 General Election.

She believes Labour leader Jeremy Corbyn will grant her a Section 30 order if he is voted in to Downing Street.

But Mr Johnson was clear he did not want to see Scots given a second vote on the country’s place in the UK.

Asked if he would ever grant permission for such a ballot, he said: “No, I don’t want to have one.”

The PM, who was speaking on Sky News’ Sophy Ridge on Sunday, said: “I think having another referendum, I don’t think people in this country think referendums are very wonderful for harmony.

“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. I don’t see any reason to go back on that, on that assurance.”

Mr Johnson spoke out after the SNP leader urged Scots to use the December 12 election to “demand the right to choose a better future”.

She told a packed rally in Glasgow on Saturday that Scotland is at a crossroads, arguing that independence is a “better alternative” to Brexit and remaining in the UK.

Ms Sturgeon told Sophy Ridge on Sunday that the issue of “who decides Scotland’s future is one of the central questions at this General Election”.

She said: “Our future is on the line and it’s a choice of what kind of future we want.”

The SNP leader claimed the PM had “omitted to recognise the fact that many things have changed since Scotland had an independence referendum in 2014, not least we face being taken out of the EU against our will”.

She insisted that if the SNP wins the most Scottish seats in next month’s election, “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”.

“I’m putting a very clear proposition before the Scottish people in this General Election and if – and I take nothing for granted – if the SNP win that election, for any Westminster politician 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,” she said.

Shadow cabinet member Rebecca Long-Bailey made clear that Labour would not block a second referendum if the Scottish Government was to push for one after the 2021 Holyrood election.

While she was clear that Labour wants “Scotland to be part of Great Britain”, she added: “Ultimately what we have said is that, after the next Scottish Government elections, if the Scottish Government determine they want to pursue another referendum and they go through the legislative process within their own government to push that forward, than as a government we wouldn’t stand in their way.”

However, Scottish Secretary Alister Jack said the Tories are 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 are “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”.

“We know that she will use any SNP success to demand a second referendum on leaving our United Kingdom,” he said.

“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.”

Scottish Liberal Democat leader Willie Rennie said Labour’s comments on a second independence referendum showed Jeremy Corbyn’s party could not be trusted to preserve the Union.

“It’s quite clear Jeremy Corbyn will break up the UK if it means he can get his hands on the keys to Downing Street,” Mr Rennie said.

“The Union isn’t something Jeremy Corbyn can barter away for personal power.

“Each and every Scottish Labour candidate should take this opportunity to tell the public whether they would vote for another independence referendum if Jeremy Corbyn instructed them to.”