This article appears as part of the Unspun: Scottish Politics newsletter.

A remarkable shift took place in Scottish politics at the weekend.

No, it wasn't Ash Regan's defection to the Alba Party.

What happened that was actually more significant was a fairly dramatic intervention by Lorna Slater.

Her comments were overshadowed by the former SNP leadership candidate's switch from the SNP to Alex Salmond's party and by the revelations over Scottish Government WhatsApp messages during the pandemic.

But what Ms Slater said on a Sunday morning interview had many an observer sit up from their coffee and Sunday papers.

She told the BBC that for the Scottish Greens independence wasn't a red line in future talks with other parties over a potential governing deal at Holyrood.

Until her remarks at the weekend it had been thought that independence was a non-negotiable for the Greens.

The Bute House Agreement struck by the SNP and the Scottish Greens in August 2021 has as one of its guiding principles the two parties shared support for that constitutional goal.

That seemed to be the party's position in July when I spoke to the Scottish Greens MSP Ross Greer. Back then he underlined that another party's opposition to a second independence referendum would be a "significant barrier" to a future Holyrood deal.

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Now, we can interpret what's going on in different ways.

Perhaps Mr Greer and Ms Slater have different views on whether independence/indyref2 are red lines. That's one possibility.

However, what may seem more likely is that, like pretty much everyone else in Scotland, the Scottish Greens have been looking at the Rutherglen by-election result, the mood among voters and the polls pointing to a significant swing to Labour.

Greens like being in government. It has helped their party's profile and helped them gain more support as well as bring greater awareness to the issues they care about.

So why, they may be thinking, hitch themselves over the long term to a party, the SNP, apparently on the wane, when it may be wiser to open the door to the one on the rise?

Behind the scenes it's understood there was some irritation with Ms Slater's comments in the SNP, though only Fergus Ewing, currently suspended from the party's Holyrood group, publicly expressed any criticism.

Certainly the SNP want to win a fifth term in 2026 and some in the party believe their chances may be boosted if a Starmer led Westminster government runs into difficulties two years into power.

Polling by the Scottish Electoral Study, published yesterday, put the SNP slightly ahead of Labour in Holyrood voting intentions though the survey pointed to a significant shift to Labour with Anas Sarwar's party six points ahead of Humza Yousaf's for the Westminster poll.

The Herald: Greens co-leader Lorna Slater said independence wasn't a red line in future talks with other parties for her party's co-operationGreens co-leader Lorna Slater said independence wasn't a red line in future talks with other parties for her party's co-operation (Image: Newsquest)
Should that momentum favouring Labour continue in the run up to the Holyrood elections they could well become the largest party in Holyrood in 2026.

Their natural partners in government, should they not win a majority, would be the Lib Dems. The two parties formed coalitions after the 1999 and 2003 elections.

But if their combined numbers do not yield a majority, they may well need help from the Greens and we could see Scotland's first "traffic light" coalition in Holyrood.

The name comes from the traditional party colours – red, amber and green – matching the sequence in a set of traffic lights. The governing arrangement has become popular in Germany with the federal government run by one such coalition headed by Chancellor Olaf Shulz, from the SPD, representing red in the traffic lights set.

Could this happen in Scotland?

It would seem that neither Scottish Labour nor the Scottish Lib Dems have closed the door to such future co-operation with the Greens.

Dame Jackie Baillie, Scottish Labour deputy leader, insisted on Monday that Labour's ambition was to form a majority government in Edinburgh after the Scottish Parliament 2016 elections. But she did not rebuff the Greens' openness.

And in the Holyrood Sources podcast yesterday the Scottish Lib Dem leader Alex Cole-Hamilton did not mention the Greens as one of the parties he would not work with in power as he declared his party "open for business" with parties "who share our values" about the future of the country.

"I can tell you that there are definitely parties I would not work with," he said. "I think both the Conservative Party and the SNP are part of the problem. They're the old politics of Scotland right now."

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Setting aside their stance on independence – which the Greens have indicated they are indeed prepared to do in any future talks – Labour, the Lib Dems and the Greens have much to agree on in terms of their outlooks and values.

There is broad agreement on the need to tackle climate change and narrow economic and social inequality. Policies on devolving more powers to local government around healthcare, more support for mental health, affordable housing and issues such as prison reform could be matters where consensus could be reached.

Slater's comments did not top the news agenda this week, but in terms of how the country is governed they may well reverberate right through to 2026 and possibly well beyond.