THE SNP must show they can be trusted if they want the Greens to support their Scottish Budget, Patrick Harvie has said.

Speaking to The National ahead of his party’s conference, the Scottish Greens co-leader said he was “seriously worried” about the direction the Scottish Government has been heading since the Bute House Agreement came to an end.

Humza Yousaf unilaterally decided to end the cooperation agreement with the Greens in April, a move which rapidly led him to resign as first minister rather than lose a vote of no confidence at Holyrood.

The resulting SNP minority government led by First Minister John Swinney and his deputy Kate Forbes will need another party’s support to pass its Budget – which will follow Labour Chancellor Rachel Reeves’s at Westminster on October 30.

READ MORE: Richard Murphy: It’s no mystery why Rachel Reeves is in a mess ahead of the Budget

In recent years, the SNP could rely on Green votes – but Harvie said there was now “a question of trust” in negotiations.

He went on: “We've seen what were already agreed as Green priorities in previous years, previous budgets rolled back. Whether that's active travel, whether that's bus pass for asylum seekers, a whole host of other areas where things that had been agreed in previous Budgets have not been followed through with.

“Then, where is the trust that can come from whatever we talk about? Whatever we put on the table in this year's Budget discussions, whatever concessions the SNP want to talk about, whatever commitments they're able to give, how can we lock those in?

“How can we agree a process that guarantees that what's put on the table stays there? That’s going to be a really important question for Shona Robison to be able to answer.”

Finance Secretary Shona Robison will deliver the Scottish Budget later in the yearHarvie said he accepted it was a “difficult question to answer”, but went on: “That question of trust, following the rollback of some things that had already been agreed, it's an important one for the Finance Secretary to be challenged on, but it's not a challenge where we're unwilling to hear the answer.”

He suggested “some kind of mechanism, whether it's in terms of parliamentary scrutiny through the committees, [or] whether it's external scrutiny through the audit processes” as one possible solution.

Reports in recent days have focused on motions to be debated and voted on at the Green conference, which will be held in Greenock over the weekend.

One motion, backed by the Green’s health spokesperson, Gillian Mackay MSP, could see the party pull support for the SNP’s plans for a “National Care Service”, while another would see Green MSPs barred from backing a Budget that includes cuts to local government funding.

READ MORE: John Swinney stands by National Care Service plans amid backlash

Harvie said that the National Care Service debate was about much more than a single Budget, while the question of council funding was more complex than it appeared and “needs to be seen in the context of additional financial powers for local government as well, so that they are less dependent … and more able to raise revenue”.

However, he suggested that progressive taxation would be a red line for his party in backing any SNP Budget.

“The Scottish Government needs to use every lever available, and that includes taxation,” he told The National.

“They know that if they want the support of a progressive political party, they're going to have to bring forward a progressive budget on the issue of tax.”

Asked if the Greens were walking something of a tightrope trying to get the SNP to commit to their policies without pushing them to rely on a different party for support, Harvie suggested the Unionists were not putting serious propositions on the table.

Scottish Green co-leader Patrick Harvie spoke to The National ahead of his party's conference (Image: Sourced) “To quote Douglas Adams: in an infinite universe, anything is possible,” he said.

“The track record of some other opposition parties in the Scottish Parliament, especially over recent years, has not been good in terms of putting forward good, positive, workable, realistic proposals … Some will just demand the impossible.”

“I think we have tried being bold, being ambitious, but being achievable in what we're trying to do.

“I actually think our politics as a whole is better if we all try and raise our game in that way, rather than just trying to score points for the sake of a headline.”

And the Scottish Green co-leader argued that they had pushed the SNP into tax decisions they had been reluctant to take – such as introducing higher income tax bands for higher earners – and been proven right.

READ MORE: Kate Forbes condemns ‘drumbeat of negativity’ about Scotland from opposition parties

“A lot of folk in the SNP were very cautious, very nervous about finally using those tax policies,” he said.

“It took us years after those powers were devolved to persuade the SNP, not just that this is necessary, but people will support this.

“I think if you demonstrate that you're applying tax fairly – and with the income tax we made sure that people on low and average outcomes were protected and even if you earned a little bit more than the average full-time salary the amount of extra tax you were paying was pennies – so long as you do it fairly … most people will support it.”

The Scottish Green conference will be held in Greenock on October 26 and October 27.