A former leader of the Scottish Greens has claimed the party has become “careless and cocky”.
Robin Harper also added it was now “really important” for Labour to get into power at both Holyrood and Westminster.
The first elected a Green parliamentarian anywhere in the UK, has hit out at the party’s co-leaders Patrick Harvie and Lorna Slater.
Harper, who was first elected as Lothian MSP in the first Holyrood elections in 1999, claimed the party leadership had been “arrogant and abrasive”.
The SNP has faced challenges from within its party over the current powersharing deal which brought the Greens into the Scottish Government.
Harper, who recently quit as a member of the Scottish Greens, told the Sunday Mail newspaper the alliance between the two parties would result in both the SNP and Greens losing votes, and it was “highly likely it will not last”.
He told the paper: “That’ll be a good thing and it is really important we get a Labour government now at Westminster and Holyrood.”
Mr Harper, who stood down from the Scottish Parliament in 2011, added: “The Green Party needs a wake-up call – they have been careless and cocky, they are not listening to people and bringing them along.”
High profile MSPs including Fergus Ewing have also spoken out saying the public “increasingly see the Scottish Greens as hard-left extremists who should never be anywhere near government”.
First Minister Humza Yousaf has insisted he is keen to keep the alliance.
Ewing voted against Slater in a vote of no confidence at Holyrood.
He previously wrote: “The SNP are tarnished, damaged and diminished by our continuing voluntary association with these hard-left extremists, and unless the deal is scrapped this will only get far worse.”
The Bute House Agreement between the SNP and Greens had pledged they would bring in policies such as a deposit return scheme (DRS) and highly protected marine areas (HPMAs) in Scotland – but both of these have had to be put on hold after coming in for heavy criticism.
Harper, meanwhile, went on to criticise the party’s current leaders, saying: “Leadership should be inspirational, it should have dignity and be rooted in plain common sense.
“The leadership that Patrick and Lorna has provided has been arrogant and abrasive, and it has repelled those who want politicians to listen and respond to other people’s ideas and feelings.”
Yousaf has defended the alliance between his party and the Scottish Greens, saying the two organisations had come together in the “best interests of our country and our planet”.
Speaking at the Edinburgh Festival Fringe earlier this week, he added that the deal allowed the Scottish Government to get legislation passed despite the “toxic environment” at Holyrood.
STV News has contacted the Scottish Greens for comment.