Opposition to a second independence referendum would be a "significant barrier" to a Bute House style deal with Labour, according to a Scottish Greens MSP who helped negotiate the party's current governing arrangement with the SNP.

Ross Greer, his party's spokesman on finance and the constitution, made the intervention as a poll last week suggested Humza Yousaf's party could lose power at Holyrood in 2026.

Six SNP MPs, including the party's deputy and former leaders at Westminster Mhairi Black and Ian Blackford, have to date said they will not be standing in the general election.

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The announcements come in the wake of a series of surveys suggesting the SNP are facing heavy losses to Labour in the electoral contest expected next year.

But while research has suggested backing for the SNP may be on the slide, the Scottish Greens have seen a boost in their support.

In an interview with The Herald on Sunday, Mr Greer, who negotiated the Bute House Agreement in 2021 with colleague Maggie Chapman, was asked if Labour opposition to a second independence referendum would be a negotiating "red line" to any governing deal with Anas Sarwar's party.

"It would be a significant barrier for us if the Labour party maintained their anti-democratic position when it comes to Scotland deciding its own future," he said.

"We are at our core as a party and a movement democrats. The Greens have a deep commitment to radical democracy and empowering people. The position of the Labour party at the moment is that Scotland can have what the Labour party wants not want Scotland's wants.

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"And I think that would be a pretty significant barrier for us to work with them. If we can't agree on the basic right of the people of this country to determine their own future it becomes hard to envisage how we can agree on a more comprehensive platform for how the country should be run."

Mr Greer also suggested there were wider policy differences other than over the constitution that could prevent the Scottish Greens forming a pact with Labour.

The Herald:

Ross Greer is the Scottish Greens' constitution and finance spokesman.  Photo PA.

He also pointed to U-turns by Labour leader Sir Keir Starmer, including rowing back on a pledge to invest £28bn a year in green industries and over North Sea oil and gas exploration.

On a visit to Edinburgh last month Mr Starmer confirmed Labour would "not grant licences to explore new fields" in the North Sea, a momentous shift for a sector which supports 200,000 UK jobs, including 90,000 in Scotland, according to trade body Offshore Energies UK.

READ MORE: Scottish Greens vote to continue with Bute House Agreement with SNP

But the party insisted it would honour any licences in existence at the time of the next election, which must be held by January 2025. That is likely to include the controversial new Rosebank development west of Shetland.

Mr Greer also criticised Labour for rowing back on a commitment for free school meals for all primary school children and said it was difficult to know what the party "stood for".

He said that ahead of last year's council elections the Scottish Greens "were very clear" that his party would work with all parties except the Conservatives.

"It was the Labour party who rejected that and have worked with the Tories in council chambers across the country to keep the Greens and SNP out," he said.

"That was the choice Labour made...as they felt their constitutional position was more important than effectively delivering services for local communities."

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He added: "Nationally it becomes harder by the day to see where we could work with Labour because their policies change every day.

"I was counting the number of policy positions that Keir Starmer has U-turned on over the last couple of weeks, including policies that are incredibly important to the Greens and our government.

"We are rolling out free school meals for all children in primary school, Keir Starmer has dropped Labour's commitment to do that, we have already delivered an emergency rent freeze and we will be delivering permanent rent controls.

"Keir Starmer has dropped Labour's commitment to do that. We are massively scaling up action to tackle the climate emergency. Keir Starmer has just dropped a £28 billion proposal to invest in the future of the [green] economy.

"His position on Rosebank specifically and on oil and gas in the North Sea entirely is at best vague but realistically to me feels like a significant step backwards. It's doubling down on fossil fuels that have no future."

Mr Greer went on to say the current Bute House Agreement between the Scottish Greens and the SNP was delivering on policies to "protect people and the planet".

He said: "It's impossible to speculate on how we could work with a party whose policies seem to change on a day by day and week by week basis. So it's for the Labour Party to sort that out.

"It's for the Labour party to tell the public, as well as other political parties, what they actually stand for and who actually calls the shots."

A poll last week found support for the SNP had slumped to its lowest level for more than 12 years in a new Scottish Parliament voting intention poll.

Seat projections based on the Redfield & Wilton Strategies survey put Mr Yousaf's party on 40 (down 24), Labour 38 (up 16), Tories 26 (down 5), Lib Dems 15 (up 11) and Greens ten (up two).

If such a result took place on polling day next year Labour and the Lib Dems would together have 53 seats and the SNP and Greens 50. The Greens could then have a key role in a Labour/Lib Dem minority coalition government should an agreement be reached among the parties, putting the SNP and the Conservatives in opposition.

Alternatively, Labour and the Lib Dem could seek a deal with the Conservatives to form a pro-Union majority government with the SNP and Greens in opposition.

Scottish Labour was approached for comment.