Party says it can overtake previous best of seven MSPs by claiming second votes of radical SNP supporters

Scottish Green party leaders expect to quadruple their number of MSPs in May’s Holyrood elections in a campaign designed to appeal to Scottish National party voters and activists.

The Greens hope to persuade tens of thousands of younger and more radical SNP supporters to give them their second regional vote in May’s elections by pledging to press for a full ban on fracking, greater land reform and to end fuel poverty.

The party campaigned alongside the SNP for a yes vote in the 2014 independence referendum. Its membership has increased tenfold since 2011, and polls suggest it may now be more popular than the Liberal Democrats.

Patrick Harvie, the SGP’s co-convenor and effective leader, said the party believed it could overtake the record total of seven Green MSPs elected in 2003 this May. “We will be campaigning on a scale and with a capacity that we have never had before,” Harvie told reporters before the manifesto launch in Glasgow.

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He said many SNP supporters were openly critical of their party’s timidity in government. “Many of the people who campaigned for the SNP want them to be bolder on issues like land reform and know that Green MSPs putting pressure on the SNP where it counts makes a difference,” he said.

The surge in membership income has allowed the party to greatly expand, now employing full-time organisers in all eight Scottish electoral regions and eight staff in its headquarters.

It has amassed a war chest of £350,000 for the May election, allowing it to mount the most ambitious campaign in its history. It has brought in campaign experts from the Australian Green party, and sent its staff to work in English and Australian Green election campaigns. Senior staff with Caroline Lucas’s general election campaign in Brighton Pavilion briefed Scottish Green activists last month.

“We’re going into this election with the capacity we have always lacked,” Harvie said. “We’ve always been aware that the polls can be kind to us and that doesn’t always materialise.

“Well, the polls are kinder to us at the moment than they’ve been ahead of any Holyrood election, but what is critically different for us is that we’ve got the capacity to reach those voters this time.”

Only two Scottish Green MSPs were elected in 2011 but the party has effective parliamentary strength of five after three MSPs quit the SNP over Alex Salmond’s decision before the referendum to support Nato membership. They now sit as independent MSPs, and two – John Finnie and John Wilson – are Scottish Green party members and Green election candidates. The third, Jean Urquhart, votes alongside the Greens but has joined the radical left campaign Rise and is standing against Finnie in the Highland region.

The Greens have suffered some damaging internal conflicts, involving candidate selection procedures in north-east Scotland, and between the candidates to become Harvie co-convenor, Zara Kitson and Maggie Chapman. But Harvie said those disputes had now been resolved.

The Greens are fighting to be included in election debates alongside the other major Holyrood parties after being given minor party status alongside Ukip by Ofcom and the BBC. Sturgeon and other party leaders are backing a petition calling for the decision to be reversed.

Harvie said his party’s growth and the SNP’s record standing in the polls at 50% or more would greatly help the Greens because of Holyrood’s mixed system of electing its 129 MSPs.

Electors get two votes: a single vote for 73 first-past-the-post constituencies, and then a vote for a regional list candidate. The system is designed to ensure smaller parties win seats proportionate to their regional support.

As the SNP is expected to win a vast majority of Holyrood’s 73 constituency seats, the system makes it unlikely that the SNP will win many of the 56 seats in the regional lists.

So the Scottish Greens are fighting a substantial “second vote” strategy to urge SNP supporters to lend the Greens their regional vote to strengthen the radical green cause at Holyrood.

To avoid alienating SNP sympathisers, Harvie will stress that the Scottish Greens will be constructive critics of the next SNP government. He said the Greens would do well “given that strategic opportunity of being able to approach people who have a regional vote that they know won’t be of much value to the SNP, but who want a political party that will speak to some of the issues that they care about.

“[Many] of the SNP members who want a bolder land reform agenda, who want a full permanent ban on fracking know that they’ll get redress on those issues just as we’ve had progress on issues like rent control when the SNP knows that the votes are not in the bag, when the SNP feel that it’s under constructive pressure from other parties.”