The co-leader of the Scottish Greens has given his backing to plans to make the next Westminster election a “de-facto” referendum on independence if the Scottish Government is blocked from holding its own ballot.

Patrick Harvie said while he would prefer for a referendum to be held, if this is blocked the next general election could be the “only ability we have then to put the question to the public”.

But he came under fire from Labour and the Liberal Democrats for his stance, with Labour MSP Sarah Boyack claiming that the “Scottish Green Party is deciding to put flags before the future of our planet”.

She hit out after Mr Harvie voiced his support for proposals outlined by Scottish First Minister Nicola Sturgeon earlier this week.

While a referendum is his ‘preferred route’ Patrick Harvie said the next Westminster election might represent the ‘only ability’ to ask Scots about independence (Rui Vieira/PA)

With Prime Minister Boris Johnson steadfast in his opposition to allowing a second independence referendum to take place, the UK Supreme Court has been asked to consider if the Scottish Government can stage its own consultative ballot.

If this is ruled as being outside of Holyrood’s powers, Ms Sturgeon has said she will make the next Westminster election a “de-facto referendum” on independence.

Mr Harvie told the Sunday Show on BBC Scotland that “very clearly” a  referendum was “the preferred route”.

But he added that as the UK Government “won’t respect” the mandate for comes from the pro-independence majority at Holyrood, if the Supreme Court ruled against a referendum “we are going to have to use the following election”.

Mr Harvie said: “I  think it is preferable Scotland’s democratic mandate is respected.

“If repeated pro independence majorities in both Parliaments isn’t enough for a mandate what on earth is? What is the democratic legitimacy they finally would respect?”

With Westminster continuing to refuse a referendum, he added: “We will go to court and we will seek permission to take that referendum forward.

“And, if the answer is no, clearly we are going to have to use the following election, that is the only ability we have then to put the question to the public.”

Plans to make the next Westminster election a ‘de-facto referendum’ on Scottish independence are a ‘dogs breakfast of a strategy’, Scottish Liberal Democrat leader Alex Cole-Hamilton said (Fraser Bremner/Scottish Daily Mail/PA)

In that election he said that Greens would “offer a distinct vision of what kind of independent Scotland we want and we would be very clear about that, just as we would in a referendum”.

Mr Harvie continued: “We would be setting out very clearly a Green vision for an independent Scotland, a specifically Green vision for an independent Scotland, and we would be accepting the premise that a majority of votes for pro-independence parties and candidates needs to be respected as a mandate.”

Ms Boyack, Scottish Labour’s constitution spokesperson, however, insisted that Mr Harvie’s comments showed that “the Scottish Green Party is more than happy to drop their environmental priorities to focus solely on independence”.

She stated: “Faced with a climate crisis, the Scottish Green Party is deciding to put flags before the future of our planet.

“This is a betrayal of the thousands of environmentalists who oppose the break-up of the UK.”

Tory net zero spokesman Liam Kerr MSP said: “The Scottish Greens have long been derided as merely an environmental offshoot of the SNP – but now we can drop the ‘environmental’ bit from that definition.

“Patrick Harvie let the mask slip by admitting the pursuit of independence trumps all else for his party – just as it does for the SNP.

“The fact that in a climate emergency the Scottish Greens are prepared to fight the next election solely on the constitution is breathtaking. And that’s if they contest it at all – Patrick Harvie hinted that they may not field candidates in order to help the SNP.

“This stance is an insult to all voters concerned about climate change and the environment, and clearly demonstrates that concern for the environment – the only thing which people thought made the Greens different from the SNP – always comes second to grievance and division for nationalists.”

Scottish Liberal Democrat leader Alex Cole-Hamilton said it was “astonishing to hear the leader of a Green party say they would go into a general election fixated on primarily on one issue”.

Mr Cole-Hamilton told BBC Scotland: “If they are not going to campaign on the climate emergency, Scottish Liberal Democrats will.”

The Lib Dem MSP described the Greens’ plans to focus on independence in the next Westminster election as a “dog’s breakfast of a strategy “, saying this it is “not going to give any clarity”.

Leading academic Professor James Mitchell, of Edinburgh University, has already said that there “no such thing as a de facto referendum”.

Speaking during the week, the politics expert said: “An election is simply not a referendum, a de-facto referendum or any other kind of referendum.”

He added: “In an election the voter is allowed to choose what he or she wishes to choose to determine their vote. It doesn’t have to be about one issue, it is rarely about one issue, but about a range of issues.

“It is not for a political party to dictate the terms of an election.”