IT’S BEEN an extraordinary rise. From 25,000 members at the start of December, in under three months the Green Party of England and Wales has more than doubled its membership to around 54,000 today.

Speaking to me in a smart north London pub, Australian-born party leader Natalie Bennett argues that the so-called Green surge is down to people looking at the three main parties and thinking: “Well, there’s really no answers there, we need something different, we need real change.”

She notes that ex-Labour and Liberal Democrat voters have been joining, along with many young people new to politics and even some former Tories concerned about fracking.

The Greens are now regularly outpolling the Lib Dems and one recent Ipsos Mori forecast even had them edging out Ukip — coming third on 9 per cent.

Turning to the much-discussed TV hustings, Bennett says: “The debate about the debates gave us a little bit of oxygen, a little bit of air, a little bit of publicity.”

She is set to represent the Greens in two of the three debates, with the final event a head-to-head between Labour’s Ed Miliband and Tory PM David Cameron.

She expects to take part in mock debates to prepare. “At the moment I’ve got a large number of people lining up to play their favourite hate figure,” she quips, adding with a chuckle that various people have also given their tuppence-worth on her wardrobe choice.

“Presentation, sadly, is an important part of politics, so we’ve got to live with that.”

In terms of the focus of the campaign itself, Bennett is keen to emphasise the party’s pledge for a £10 an hour minimum wage by 2020 — £2 more than the Labour Party.

With improved wages, the Green leader also wants “jobs you can build a life on — that means no zero-hours contracts, full-time if you want full-time.”

More broadly, she points to the party’s broad anti-privatisation agenda, reversing NHS sell-offs and bringing the railways back into public ownership.

She talks about promoting walking and cycling, local bus services and giving people viable alternatives to the car. “We’ve announced we’d like to take a significant proportion of the funds this government would like to spend on road building and put it in to cutting train and bus fares by 10 per cent, helping encourage people on to more sustainable forms of transport.”

This, she explains, “would also tackle air pollution issues, which would also tackle health issues.”

Bennett has good reason to be optimistic. Website Vote for Policies, which polls visitors on issues without giving away party stances, puts the Green Party ahead of everyone else. She also notes a November YouGov survey suggesting that 26 per cent of people would vote Green if the candidate had a chance of winning in their constituency — that’s third behind the Tories and Labour.

But it’s not all been plain sailing and the party’s policy of a “citizen’s income” of £72 a week paid to every adult to replace the current benefits system received a media mauling for its harsh treatment of the poor — with Green Party MP Caroline Lucas denying earlier this month that it would make the manifesto.

But Bennett sings a different tune. “It will be in the manifesto,” Bennett tells me, adding that it will be fully costed but remains a long-term aspiration that would take more than one Parliament to implement.

We don’t have time to go into the detail of the criticism, but she insists: “People really need a sense of security and that’s one of the things citizen’s income can offer.”

The party’s position on prostitution — the so-called New Zealand model of decriminalisation — has also come under fire.

While Bennett accepts that many well-meaning people support a Swedish-style outlaw, she argues that decriminalisation is “supported by sex workers and unions representing sex workers” and is the model which “can keep vulnerable women and men most safe.”

It’s another thing that puts her at odds with sole MP Lucas, who supports the Swedish model. “The Green Party doesn’t whip,” Bennett explains. “We believe in grown-up politics. We can cope with that.”

As well as hoping to hold Lucas’s Brighton Pavilion constituency, the Green Party has a number of other target seats in May, including Norwich South and Bristol West. Bennett herself is standing in Holborn and St Pancras in London.

But given Britain’s creaking first past the post (FPTP) electoral system, there is a strong possibility the Green surge will not translate into any additional MPs. Unsurprisingly, this frustrates Bennett.

“One of the key things that I think is certain to come out of this election is that FPTP is going to be a certain loser,” she says. “I think there will be a strong push for electoral reform” because “quite a lot of people for who electoral reform has never crossed their lips are going to find their local MP has been elected with not much more than 25 per cent of the vote.”

While the Green Party may not gain any more MPs, the recent Guardian data-crunching predicted an increase in the Green vote could make a Tory win more likely. Bennett pushes for a wider analysis: “I think we have through generations in Britain been trained by FPTP to vote for something that wasn’t what we really wanted, sometimes the thing we disliked the second most, to stop the thing we really hated getting in.

“That’s actually what has given us the kind of politics we have now. It means you have a Labour Party that is pretty hard to distinguish from the Tory Party — certainly in terms of policy if not necessarily always in rhetoric. If voters keen doing the same thing they are going to keep getting the same kind of politics.”

Her simple solution is to encourage voters to ditch tactical voting: “It’s possible to have a peaceful political revolution if voters decide to vote for what they believe in.”

I opt to end the interview with a few personal questions. James Meek’s critique of privatisation Private Island, Tim Jackson’s Prosperity Without Growth: Economics For A Finite Planet and the ground-breaking Spirit Level: Why Equality is Better for Everyone are her non-fiction suggestions for voters, while the most “ungreen” thing she does is to take a long shower.

But, a seasoned interviewee, she turns the question round to party policy. “What we want to see is structural change that makes the environmentally friendly thing to do the easiest and cheapest and simplest thing to do.

“So it’s not a case of telling individuals they should change their behaviour.

“We need to change the whole way society works.”