The Greens could displace the Liberal Democrats as the main centre-left challengers to Labour as they prepare to field more than 500 candidates at next year’s general election, their only current MP forecasts.

Caroline Lucas said the Greens will stand 200 more candidates than at the last election and they plan to target 12 key seats. The “Green surge” comes as the party seeks to capitalise on soaring membership and strong opinion-poll ratings which have brought its support close to that of the Lib Dems.

Its priority will be to defend Ms Lucas’s Brighton Pavilion seat and the party will pour heavy resources into capturing two constituencies – Bristol West and Norwich South – held by the Lib Dems.

Ms Lucas said the Greens were prospering from a continuing backlash against the Lib Dems for entering a coalition with the Conservatives and for breaking their promises over university tuition fees. Her party collected 150,000 more votes than the Lib Dems in this year’s Euro-elections – and three MEPs to Nick Clegg’s one – and outpolled them by five to one in last week’s Rochester and Strood by-election.

She said the groundswell of support meant she could now foresee the Greens becoming Labour’s principal rival for the anti-Tory vote.

“I can envisage that, notwithstanding the fact that there are some good and honourable people within the Lib Dem party and some of their MPs. The decision to have gone into the Coalition Government with the relish which they did has meant people who looked to the Lib Dems to provide an alternative feel incredibly let down.

Policies: Where the Greens stand on the major issues Show all 13 1 /13 Policies: Where the Greens stand on the major issues Policies: Where the Greens stand on the major issues Taxes Wealth tax of up to 2 per cent on the assets of 300,000 people who are worth more than £3m, the country’s richest 1 per cent Corbis Policies: Where the Greens stand on the major issues Wages National minimum wage to be lifted to living-wage levels and to reach £10 an hour by 2020. Would also “curb boardroom excesses” by linking salaries at the top of companies to pay at the bottom Getty Policies: Where the Greens stand on the major issues Pensions End pensioner poverty by introducing a weekly “citizen’s pension” of £170 for a single person and £300 for a couple Getty Policies: Where the Greens stand on the major issues Energy Targets and timetables for improving efficiency and reducing greenhouse-gas emissions across all sectors. Wants electricity use to be reduced by a third by 2020, by half by 2030 and two-thirds by 2050 REX FEATURES Policies: Where the Greens stand on the major issues Health Accuses Labour and Tory governments of introducing privatisation by stealth into the NHS. Pledges to “maintain a publicly funded, publicly provided health service” Getty Policies: Where the Greens stand on the major issues Education Money would be allocated to schools according to their needs rather than their status. Schools which remain in the private sector would be classed as businesses, have all charitable status removed and pay taxes Getty Policies: Where the Greens stand on the major issues Railways Bring railway network back into public hands as franchises expire or if companies break the terms of their agreements Getty Policies: Where the Greens stand on the major issues Immigration Rules would be “based on the principle of fair and prompt treatment of applicants rather than on excluding dishonest applicants whatever the cost to the honest ones” Getty Images Policies: Where the Greens stand on the major issues Food Minimise transport of food and other agricultural products by supporting local food distribution and pressing for transport costs, especially air freight, to fully reflect environmental impact Creative Commons Policies: Where the Greens stand on the major issues Farming Phase out all “factory farming” and support a transition to small, free-range units, mixed rotational farming and extensive grazing. Would ban battery farming of poultry Getty Policies: Where the Greens stand on the major issues Genetic engineering Moratorium on the release of genetically modified organisms (GMOs) into the environment and on the importation of food and feed containing GMOs, pending comprehensive assessment of the technology’s safety Getty Policies: Where the Greens stand on the major issues Cannabis Possession, trade and cultivation of cannabis would be immediately decriminalised. Trade in cannabis would be examined by a Royal Commission, with a view to establishing a fully legalised and regulated trade Reuters Policies: Where the Greens stand on the major issues Housing Reform housing benefit to give greater help to poorer tenants and to prevent eviction or repossession of either private tenants or homeowners Getty

“The corrosiveness of what’s happened goes beyond saying one thing and doing another; saying they won’t increase tuition fees and trebling them,” Ms Lucas said.

“It’s also gone to the heart of the people’s disillusionment with the whole party political process in the sense that you can’t believe politicians any more. I can’t forgive them for the sense they have brought politics into even greater disrepute than it already was.”

The party is drawing support from across the political spectrum and is polling particularly strongly among younger voters. Its membership has almost doubled to more than 25,000 since January.

The growth is regarded by some MPs as mirroring the dramatic success of Ukip on the right and the party’s potential to siphon votes from Labour has prompted Ed Miliband to order moves to win back Green voters.

The Greens’ increased confidence is reflected by their ambitions to capture seats in Norwich, where the party has historically been strong, and Bristol, which has been designated Europe’s “green capital” next year.

Natalie Bennett, the party’s leader in England and Wales, said yesterday: “What’s happening is the safe seat is practically disappearing. There is a really good chance that 25 per cent of the vote might win quite a lot of seats with the votes split four ways.”

The party is also focusing on another nine seats where it believes it can perform strongly. They include three other Lib Dem-held constituencies – Cambridge, St Ives and Solihull. The Greens also have five Labour-held seats in their sights – Holborn and St Pancras, which is being contested by Ms Bennett, Sheffield Central, Liverpool Riverside, Oxford East and York Central. Finally, it is targeting Tory-held Reading East.

The party only received around 1 per cent of votes at the last election, but made a crucial breakthrough when Ms Lucas became the first Green to sit in the Commons.

Ms Lucas, who had previously represented the Greens at Strasbourg, said her arrival at Westminster gave the party an “absolutely massive” boost to its domestic credibility. And she said the turbulent political landscape meant it was possible that Westminster was heading towards an historic realignment of power.

“The Green Party could continue this positive but relatively incremental growth, so in 2020 I would very much hope there would be half a dozen MPs here in Parliament. But I get the sense we could be on the edge of something very big and very different – the three main parties are between them accounting for less and less of the overall vote,” she said.

“The plates are moving. There’s certainly a scenario where some of the bigger parties recognise a more proportional system might be in their interest, in which case all bets could be off, and that could be incredibly exciting.”

Ms Lucas acknowledged that the Greens had been here before when they stunned the major parties to come third in the 1989 European elections before sliding back into semi-obscurity.

But she insisted: “We are learning from that this time around. The party now is an awful lot more professional than it was then. We have more staff with experience and hopefully we will be able to build on the phenomenal growth we have seen in the last 12 months.”Employment

“Green new deal” to create one million jobs in renewable energy, insulation, social housing, public transport and waste management.

Policies: Where the Greens stand on the major issues

Taxes

Wealth tax of up to 2 per cent on the assets of 300,000 people who are worth more than £3m, the country’s richest 1 per cent.

Wages

National minimum wage to be lifted to living-wage levels and to reach £10 an hour by 2020. Would also “curb boardroom excesses” by linking salaries at the top of companies to pay at the bottom.

Pensions

End pensioner poverty by introducing a weekly “citizen’s pension” of £170 for a single person and £300 for a couple.

Energy

Targets and timetables for improving efficiency and reducing greenhouse-gas emissions across all sectors. Wants electricity use to be reduced by a third by 2020, by half by 2030 and two-thirds by 2050.

Health

Accuses Labour and Tory governments of introducing privatisation by stealth into the NHS. Pledges to “maintain a publicly funded, publicly provided health service”.

Education

Money would be allocated to schools according to their needs rather than their status. Schools which remain in the private sector would be classed as businesses, have all charitable status removed and pay taxes.

Railways

Bring railway network back into public hands as franchises expire or if companies break the terms of their agreements.

Immigration

Rules would be “based on the principle of fair and prompt treatment of applicants rather than on excluding dishonest applicants whatever the cost to the honest ones”.

Food

Minimise transport of food and other agricultural products by supporting local food distribution and pressing for transport costs, especially air freight, to fully reflect environmental impact.

Farming

Phase out all “factory farming” and support a transition to small, free-range units, mixed rotational farming and extensive grazing. Would ban battery farming of poultry.

Genetic engineering

Moratorium on the release of genetically modified organisms (GMOs) into the environment and on the importation of food and feed containing GMOs, pending comprehensive assessment of the technology’s safety.

Cannabis

Possession, trade and cultivation of cannabis would be immediately decriminalised. Trade in cannabis would be examined by a Royal Commission, with a view to establishing a fully legalised and regulated trade.

Housing