Steadily climbing in the polls and surging in membership numbers, the Greens are the only party promising “real change” to disillusioned left-leaning voters, their leader has claimed – as she called for new taxes on the super-rich and the renationalisation of the railways.

Speaking ahead of the party’s annual conference, Natalie Bennett also attacked broadcasters for failing to give her party a fraction of the coverage they have provided for the “dangerous and divisive” Ukip. The Greens, who gained three MEPs in this year’s European elections, are averaging 6 per cent in the opinion polls – 3 points behind the Liberal Democrats and just under half the support currently enjoyed by Ukip.

In an interview with The Independent, Ms Bennett said the party was determined to defend its sole parliamentary seat, Brighton Pavilion, at next year’s general election and disclosed it also would pour resources into capturing seats in Norwich and Bristol.

She claimed that traditional loyalties on the left were splintering, with the Greens winning a stream of previous Labour and Lib Dem supporters, as well as large numbers of voters aged between 18 and 35. Membership has risen by 28 per cent to more than 18,000 this year.

“People are feeling this profound sense of dissatisfaction with business as usual,” she said. “People really understand, often perhaps no more than at a gut level, that we need something different, we need real change. People are actively seeking us out. We are just different and people want something different.”

The party is calling for a wealth tax of up to 2 per cent on multimillionaires with assets of more than £3m – a levy that could raise as much as £43bn.

“Now is the time to seize from the 1 per cent – the richest people who have been running society for their own benefit – to restructure so we are very much focusing on a society that works for a common good,” Ms Bennett said.

“This isn’t a penalty – this is recognition of the fact that they are people who have benefited from society, benefited from collecting the wealth of society.”

The Greens are backing the renationalisation of railways, the reversal of Coalition health service reforms, the scrapping of the welfare cap and the introduction of community-run schools. They also strongly oppose “fracking” and the construction of the HS2 rail-link, and are calling for heavy investment in renewable energy and energy conservation schemes.

Ms Bennett said the Greens’ conference, which begins tomorrow in Birmingham, would see the party “stepping up for the election”. She said: “It’s a different election from any we have had before because we’re fighting it as a parliamentary party.”

She claimed her party was well-placed to hold on to the Brighton seat won by her predecessor, Caroline Lucas, at the last election despite the negative headlines about the Green administration in the Sussex town’s council.

She also predicted gains in two Liberal Democrat-held seats in Norwich South and Bristol West, where the party has performed strongly in local elections. Ms Bennett said she was frustrated by the lack of media attention for the Greens compared with Ukip and appealed to broadcasters to give the party more airtime. “It’s partly because Ukip has a very simple message that is easy to fit into a tabloid headline or a tabloid sentence. In the Green Party we understand the world is a lot more complicated than Ukip paints it as. .

“If you look at the figures – depending on what poll you look at – we’re often polling a third to a half of the Ukip vote. For the moment we’ll settle for a third to a half of the Ukip coverage.”

And she delivered a scathing verdict on Nigel Farage’s party which, she said, was reaching out to “angry frustrated people”.