"Obviously I hope we're going to get some good results..." says Scottish Green co-convenor Patrick Harvie, reflecting on a general election he admits is a "tough gig" for his party.

But what would count as a good result, come Friday morning? He laughs. The Scottish Greens have earmarked two target seats - Edinburgh East and Glasgow North. In 2010, they won just five per cent and three per cent of the vote respectively in the constituencies. Asked whether winning is a realistic prospect, Harvie replies: "We are going to make the best case that we can to the voters in those constituencies and all the others that we're standing in."

That will be a no, then. Although the MSP does not utter the word. A first past the post voting system, which "bullies people into picking between two parties" and a crowded field with the SNP offering a strong alternative for those dissatisfied with the Westminster establishment are cited as significant barriers for the Greens.

Mr Harvie recently spent time campaigning in Bristol West, a target for the separate but affiliated England and Wales party, and Brighton Pavilion, held by Caroline Lucas since 2010.

He said in the seats, ones "not burdened by the purple menace", the Greens offered the obvious alternative to Labour, LibDems and Tories. Clearly, the same cannot be said for Scotland.

But if you thought this meant doom and gloom, think again. While the national polls put the party at around three per cent in Scotland, that compares to 0.7 per cent it won in 2010. It is standing in the majority of constituencies for the first time, and Mr Harvie says he hopes it will be the last occasion that they do not have a candidate in every seat.

More significantly than that, though, is what he describes as an "incredible membership surge" following the referendum campaign in which the party argued in favour of independence and Harvie's profile increased significantly.

This time last year, there were 1,500 card-carrying Scottish Greens, the figure has since risen to almost 9,000, far outstripping the Scottish Liberal Democrats. Around 40 per cent of the membership are aged under 30, offering a vibrancy and creativity that rivals lack. New branches have sprung up across the country, while former SNP backbenchers John Finnie and John Wilson have joined the party, remaining independents at Holyrood for now but standing as Greens next year.

In the current campaign, groundwork is being laid for the future, with a strong Green election machine creaking into gear for the first time. Polls for next year's Scottish Parliament election, in part decided through a proportional representation system, have suggested that 11 Green MSPs will be taking seats at Holyrood, compared to two currently. A Green group in the double figures is a realistic target, Harvie says, with his new recruits able to convert impressive polling into votes.

"We've always been aware at previous Holyrood elections that sometimes we poll quite well and it hasn't always turned into Xs on pieces of paper," he adds. "We've often put that down to our lack of capacity on the ground to run local campaigns in communities and actually reach the voters. Well, that's not an excuse we can use anymore... We've got the resources, both human and financial, we've always been lacking."

He sees his party as having a vital role in holding the SNP to account, criticising both Labour and the Nationalists for a tribal approach he describes as "one of the most damaging things about Scottish politics".

He is critical of "obedient lobby fodder", saying parliamentarians' primary focus should be to hold the powerful to account, rather than batting for a particular team. A motion passed at the recent SNP conference, banning public dissent from party policy by its elected members, is "not a healthy sign," he says.

Mr Harvie says: "One of the clearest examples is the attempt to get minimum pricing of alcohol through. The SNP were proposing that, recognising it was a new proposal and you could only know how effective it was going to by trying it. The Labour Party were proposing similar measures on caffeinated alcohol products.

"Both were putting forward good, creative, constructive policies - and they both saw success as shooting down the other's good idea. They didn't see success in uniting together to achieve something collaborative. That hostility, that tribalism, meant a much weaker bill than we needed to have."

He adds: "It gives us a clear strategic opportunity as a party willing to be constructive where we can be, challenging where we have to be, and capable of holding the SNP to account. Because when we criticise something they're doing, it's because of the thing they're doing, not because it's the SNP."

But while it is clear the Greens have one eye on 2016, the current general election is not being dismissed as an afterthought. Mr Harvie has high hopes that his party's policies over TTIP and fracking, which go further than the SNP by supporting outright bans, will attract strong support.

On oil, he differs from the SNP completely. He does not bring up many of the more radical propositions in the Scottish Greens' manifesto, such as a citizens' wage, but when asked whether he would describe himself anti-capitalist, her says he would not object to the description.

He admits: "In many ways saying you're anti-capitalist is like saying you're anti-gravity" given the dominance of the "unsustainable" model, but that does not put him off exploring what system might emerge in its place.

Don't expect any Scottish Green MPs to be making the anti-capitalist argument on the floor of the Commons any time soon. But the battle-scars won by fledgling members in the current campaign may have laid strong foundations for the battles ahead.