Boris Johnson has insisted he will never grant a second Scottish independence referendum - amid fears Jeremy Corbyn has done a back room deal with Nicola Sturgeon to sneak into power.

The Prime Minister said the 2014 ballot - when Scots voted to stay in the union - was a 'once in a generation' decision.

Pressed on whether he would authorise a second referendum, he replied: 'No, I don't want to have one. I don't see any reason to go back on that assurance.'

The defiant retort, in an interview on Sky News' Ridge on Sunday, comes as the SNP ramps up its demands for another vote north of the border.

To make the result binding the Scottish government would need approval from Westminster. However, Mr Corbyn has made clear Labour will not 'stand in the way' of a referendum, which Ms Sturgeon has insisted will be a red line for propping up a minority Labour administration after December 12.

In an interview on Sky News today, Boris Johnson said the 2014 ballot - when Scots voted to stay in the union - was a 'once in a generation' decision

Nicola Sturgeon (pictured at a rally yesterday) has insisted a second IndyRef will be a red line for propping up a minority Labour administration after December 12

Asked about the idea of another showdown said: 'I think having another referendum, I don't think people in this country think referendums are very wonderful for harmony.'

He added people were told the 2014 vote was a 'once-in-a-generation event'.

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 insisted 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.'

Former Scottish Tory leader Ruth Davidson said Mr Corbyn and Ms Sturgeon 'might be cooking up grubby backroom deals'.

But she warned more referendums are not the answer to the 'current constitutional wrangling'.

Ms Davidson added: 'The people of this country are quite frankly sick to the back teeth of politicians fighting between themselves while ignoring the instructions they were given. 'Scotland voted to stay part of the UK and the UK voted to leave the EU.'

During the interview, Mr Johnson said it was a matter of 'deep regret' he did not deliver on a promise to leave the EU on October 31.

Asked if he was sorry for missing the Halloween deadline, he said: 'Yes, absolutely.'

When pushed if he would apologise to members who voted for him on the basis he would have sorted Brexit by the end of last month, he said: 'Of course, of course. It's a matter of ... it's a matter of deep regret.'