The Scottish Greens decision to join the SNP government appears to have done them "no harm at all", according to a leading polling expert.

Professor Sir John Curtice said being a junior partner in a government can be a “painful and difficult” experience – pointing to the example of the LibDems, who more than a decade on have yet to recover from entering a coalition with the Tories at Westminster.

But he said so far the decision of the Scottish Greens co-leaders Patrick Harvie and Lorna Slater to take two junior ministerial positions in the Scottish Government – which was branded a “coalition of chaos” by the Tories – does not seem to have done the party "any harm at all".

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Writing in a blog post published before the Scottish Greens conference last week, he explained: “Since the agreement between the two parties was announced at the very end of August last year, the party’s poll rating for the Holyrood regional list vote has averaged 11%. 

“Not only is this up on the 8% that the party secured in last May’s election, but it continues to match at least the ratings the party was enjoying during the previous parliament. 

“The party’s supporters have evidently not taken umbrage at its new role.”

Curtice said this should not be a surprise as while the party is focused on environmental issues, in practice its support is shaped by the constitutional debate.

He added: “The Greens were already tied to the electoral hip of the SNP, and consequently many of their supporters probably regarded the arrangement between the two parties as a natural fit. 

“Certainly, shortly after the cooperation agreement between the two parties was announced Opinium found that 94% of Green supporters thought that it would be ‘good for Scotland’.

“Recent polls show no sign of any change to these patterns. On average, they suggest that the party enjoys 17% support on the list vote among current Yes supporters, while just 3% of No voters are backing the party. 

“Similarly, around 17% of those who would vote for the SNP on the constituency vote say they would vote Green on the list.”

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However, Curtice cautioned the Scottish Greens will face a challenge in winning seats at the local elections in May under the Single Transferable vote system, which means a higher level of support is required than to claim a regional list seat at Holyrood. 

He added: “Thus, although the party contested just over 60% of Scotland’s 354 wards at the last local elections in 2017, the 4% of the total first preference vote that it won garnered it just 19 seats, of which all bar four were gained in Edinburgh and Glasgow. 

“The question mark that faces the party this time around is whether it can make enough of an advance to obtain a significant local government presence outside the country’s two largest cities – and whether it might be assisted in that endeavour by transfers from first preference SNP supporters.”