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

The Bute House Agreement is again in the public spotlight as the political parties gear up for the general election expected later this year.

It will be the first time the SNP and Greens have campaigned against each other at a national level while formally working together in government and the dynamic between the two parties is being closely watched by political observers.

The Greens did stand in the Rutherglen and Hamilton West by-election back in October. But such was the huge scale of the Labour victory then that the decision by the smaller pro-independence party to stand made little difference to the result.

Labour took 17,845 votes, the SNP 8399 and the Greens 601. The SNP would have been heavily defeated anyway even had the Greens decided not to enter the race and all of their votes gone to the SNP.

SNP politicians will be crossing their fingers that the voting behaviour in Rutherglen won't be replicated in any fashion in any parts of Scotland when the country heads to the polls this autumn and that the party can hold onto the large leads it took in 2019 over its nearest rivals.

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UnspunCurrent relationship status between SNP and Scottish Greens? It's complicated

But opinion polls published in recent months, including by YouGov today, suggest any wish that the SNP will retain its considerable dominance in Scotland is probably unrealistic.

The latest poll by YouGov put Labour two points ahead of the SNP in terms of Westminster voting intentions with the former party on 33% compared to 31% for the latter.

But a mega poll by the same company which gave detailed seat-by-seat research brought very grim news for the SNP predicting the party would fall to 19 seats, a substantial drop on the 48 won in 2019.

According to that poll, most of the central belt would turn red with the SNP holding on to seats in Stirling, Perthshire and the Highlands.

Against this change in the SNP's fortunes, the news that their junior partners in government would be standing against them in 32 out of 57 seats was, to put it mildly, not welcome.

Tensions are very much in the air.

The First Minister declared yesterday that a vote for the Scottish Greens at the forthcoming general election would be “wasted”.

Scottish Greens MSP Ross Greer hit back accusing the SNP of being “unwilling to step up when needed to protect our common future”.

His comments then prompted long-serving SNP MSP Fergus Ewing to renew his call for his party to withdraw from the Bute House pact – and to do so before the general election campaign got fully underway.

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Fergus Ewing: How can we be partners with a party whose leaders routinely abuse us?

“Our Green 'partners' are now urging voters not to vote SNP. They are contesting seats against us, which will cost several of our MPs their seats,” wrote Mr Ewing.

“This dire deal is destroying the party... Message to Humza: “Sorry mate: Failing to terminate this dreadful deal is political insanity and electoral suicide.”

So will the deal crumble in the weeks ahead?

The sense around Holyrood is “probably not”.

The Herald: The next general election will be the first time the SNP and Greens have campaigned against each other at a national level while formally working together in governmentThe next general election will be the first time the SNP and Greens have campaigned against each other at a national level while formally working together in government (Image: Newsquest)
However strong Mr Ewing wants the First Minister to call time on the agreement, the general feeling is that it is likely to limber on until the Westminster election, which will probably be held in October, if the Chancellor Jeremy Hunt's hints are correct.

The problem for Mr Yousaf is that he staked his leadership bid on the deal with the Greens continuing and can't withdraw from it now without being seen as weak and panicky.

Some in the party believe the day of reckoning for both Mr Yousaf and the Bute House Agreement will be polling day itself.

The SNP conference last October agreed that winning a majority of Scotland’s 57 Westminster seats next year – ie 29 – would constitute a mandate for independence talks.

That number sets the marker for victory for the party, the implication being that Mr Yousaf's position as leader – and the Bute House Agreement – would be safe should the SNP reach or exceed that number.

But what if the SNP don't win 29 or more seats come the election? What then?

One report in the Sunday Times this month suggested that Mr Yousaf would remain as leader of the party come what may.

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“Humza is going f***ing nowhere after the general election,” a loyal SNP figure told the paper.

And a more critical figure in the party agreed: “Humza won’t resign and there is nobody at Holyrood who will oust him.”

It's not a view shared by others.

There is a feeling in the party that while a poor result may be understandable under the cloud of the ongoing Operation Branchform investigation, Mr Yousaf would have to go if disaster hits on election night.

On that thinking the SNP would then have 18 months for the party to launch anew under a new leader, turn a leaf on the Sturgeon era and probably consign the Bute House Agreement to history.