Paul Sweeney, the party’s shadow Under Secretary of State for Scotland, confirmed the agreement could be hatched in exchange for the Nationalists’ support in putting Jeremy Corbyn into Downing Street if there is a hung parliament, while Scottish Labour leader Richard Leonard confirmed the party would not block a second referendum if there is a pro-independence majority after the 2016 vote.

Scotland would vote for independence if Brexit goes ahead, new poll suggests

The comments were seized on by Tories as evidence of an “SNP-Labour alliance” being drawn up just days before the election is held.

Scottish Labour leader Richard Leonard (top right) confirmed an agreement could be hatched in exchange for the Nicola Sturgeons party supporting Jeremy Corbyn in a hung parliament. Pictures: John Devlin/JPIMedia/PA

Nicola Sturgeon confirmed again yesterday she is “offering support” to a minority Labour administration – but the price would be an independence referendum next year.

Section 30 order

The SNP leader is to seek a section 30 order from the new Prime Minister before Christmas to transfer power from Westminster – which has power over the constitution allowing a referendum to be staged on independence.

Mr Sweeney hinted this could happen after the next Holyrood election in just 16 months.

“We’re democrats and we respect the right of the Scottish people to self-determination,” he told the BBC’s Politics Scotland yesterday.

“It’s a common ground which established the Scottish Parliament in the first place.

“If there was an explicit mandate, say after the Scottish Parliament election in 2021, then it wouldn’t be for any British government to stand in the way of that.

“And David Mundell, for the former Secretary of State for Scotland, is actually in agreement with the position. It’s actually a common ground across all parties in the UK that would be the situation if there were an explicit mandate. There certainly isn’t one just now in our view and that isn’t something we’d be going into at this stage.”

He insisted there has been no talks with the SNP on this issue at the moment.

Holyrood 2021 vote

Asked if pro-independence parties winning a majority at Holyrood in the 2021 vote would see Labour back a second referendum – in return for SNP backing for a minority Labour Government – Mr Sweeney added: “It’s a possibility, certainly.”

He insisted no formal arrangements were in place, but pointed to Tory claims that if there was an explicit mandate in the next Holyrood election it’s not something a UK government could stand in the way of.

Scottish Secretary Alister Jack appeared to accept this in a November interview, but has since backtracked and ruled out Tory support for a second referendum at any time.

Jeremy Corbyn has insisted that he would not grant a second referendum in the early years of a Labour government.

But Mr Leonard sais yesterday the “battle” over the holding of another referendum would be “won or lost in Scotland”, during the Holyrood elections in 2021 or beyond.

He added: “If as a result of those elections, as there was in 2011, there was an overwhelming majority and a clear demonstration of support for a party that was in favour of holding a second independence referendum, then Jeremy Corbyn has said a UK government will not block it.”

'Labour-SNP pact'

And Scots Tory leader Jackson Carlaw insisted that a Labour-SNP alliance has now been confirmed.

“Paul Sweeney has set it out in black and white,” he said.

“A Labour-SNP pact is being drawn up; it’s just a matter of dotting the i’s and crossing the t’s. This is what could happen by Friday if Sturgeon and Corbyn succeed.”

“It means our Union is on the line this week. Ian Blackford said today that he and Jeremy Corbyn speak regularly, and he doesn’t expect Corbyn to oppose the Nationalists. So pro-UK voters in Scotland face the very real risk of an Indyref2 pact being stitched up by the end of this week.

“Pro-UK voters in Scotland must act on Thursday to stop this happening. And it is only by voting Scottish Conservative and Unionist that we can do that.”

Nationalists say there is already a mandate for a referendum after the 2016 result which returned a pro-independence majority of SNP and Green MSPs. Opponents say conditions in the Green manifesto, including a one million-strong petition, have not been met to trigger a second vote.

SNP support

Ms Sturgeon warned yesterday that if Labour seek to govern without a majority after a hung parliament, the party “would then have to get support to get their policies through”.

She added: “I would be offering that support.

“I don’t believe Labour, if against all the odds and what the opinion polls say, they get into a position to govern and implement their manifesto, they would turn their backs on that.

“My view here is that they should think about that prospect and imagine that on Friday Jeremy Corbyn and John McDonnell are in a position of being able to form a government, I don’t think they’re going to turn their backs on that.

“If they do, I think they’ve got some big explaining to do.”

And SNP Westminster leader Ian Blackford added: “I know Jeremy Corbyn well, I have meetings with him on a regular basis, I know that Jeremy has supported the right of self-determination right around the world.

“There’s no reason why he would not recognise that the mandate is not already there and that he has to compromise on that position.

“For us it’s very simple the legislation is going through the Scottish Parliament just now, we need to have that referendum in 2020.”

“I’m simply saying to Jeremy Corbyn and anyone else – respect democracy, respect that mandate is already in place. Let’s have realistic talks about transferring that power to the Scottish Parliament.

“The Parliament on behalf of the Scottish people can then determine the timing of that. We want that referendum to take place in 2020 then we can move on.”

Scottish Independence: Labour open door to SNP deal for indyref2