Derek Mackay could try to secure next year’s budget without the Scottish Greens after the party made a politically hazardous overhaul of local taxation its red line for entering talks.

One option would be to rely on the two LibDem MSPs for Orkney and Shetland, who voted for the last budget because of a £10.5m investment in local ferry services.

The support of Liam McArthur and Tavish Scott would have enabled the SNP minority government to secure its budget by 64 votes to 62, even if the Greens had opposed it.

A Scottish Government source said the experience had demonstrated there were “interesting options” available, adding: “There’s more than one way to skin this cat.”

Green MSP Andy Wightman also admitted the budget could pass without his party if the finance secretary won over MSPs with “pork barrel” spending in their constituencies.

He told The Herald: “Last year did demonstrate the government can rely on the support of constituency members on matters of importance to their constituents.

“They got those two votes from the Liberals. Had we voted against the budget, they’d have got the budget through. So they didn’t need us. Now they know that.”

If Mr Mackay again made the Northern Isles MSPs an offer they couldn’t refuse, it would give him 64 votes out of 128 (the Presiding Officer does not vote except in a casting vote).

If the former SNP minister Mark McDonald, who now sits as an Independent, also backed the budget, Mr Mackay would then have an absolute majority in Holyrood for his plans.

The Greens negotiated extra spending in return for supporting the last two budgets.

However they are adamant they will not negotiate on the 2019/20 budget without meaningful progress on replacing council tax and giving councils more tax powers.

They want a fundamental shake-up of council finance, bringing it into line with the European norm, with local authorities raising around half of their own spending in tax.

However Mr Mackay has so far given no sign that he is willing to accede, fuelling speculation at Holyrood about other options.

A government source said: “People are aware of options when we get to critical votes.

“The attraction of the Greens is that we don’t have to be negotiating for every single vote.

“But it’s a fact of arithmetic and political reality that it’s not the only route.

“Some other routes might be less attractive, and harder work. But there’s more than one way to skin this cat.”

Mr Wightman said: “At the end of the day it’s a decision for Derek Mackay. He’s got to decide how he plays this.

“We’ve made our position very clear. The problem with the SNP on this is that they’re not making commitments for one budges - in fact nothing we’re asking for would be incorporated in a finance bill - everything is about commitments for the longer term.

“That involves cabinet sitting down and thinking about the next election, thinking about their manifesto, and thinking about the kind of commitments that they can make.

“On local tax we’re doing no more than asking them to confirm [a previous commitment] that council tax should end.

“It shouldn’t be too hard for them, in our view, to say that, but somehow it is.”

LibDem leader Willie Rennie last weekend said he would not enter budget talks because the SNP would not meet his precondition of shelving a second independence referendum.

A LibDem source said that made it unlikely Mr McArthur or Mr Scott would vote for the budget, although no decision had been taken.

The LibDems also expect the one-year ferry funding from 2018/19 to be continued next year, so Mr Mackay would not be able to dangle that particular carrot a second time.“We’re not interested in pork-barrelling from one budget to the next one, said a source.