A surge in support has made the Green Party a potentially disruptive anti-austerity political force in what is set to be Britain's most unpredictable election, even if it wins only a few seats.
As she spoke to voters in London, Australian-born party leader Natalie Bennett said the Greens had been boosted by the electoral triumph of Greece's Syriza.
"This could be the election where the future of British politics looks nothing like the past," Bennett, a former journalist running for election to the Holborn and St Pancras constituency, told AFP.
The party's support has steadily risen over the last year and broke into double figures in two January polls, drawing from mostly younger voters disillusioned with mainstream politics and angry at the government's public spending cuts.
Membership of the party, which holds a single seat in parliament, doubled to 51,000 in three months, overtaking junior coalition partner the Liberal Democrats and the anti-EU UK Independence Party.
But Britain's voting system means even if smaller parties have significant support nationally, they will not win seats in parliament in May unless they dominate individual constituencies -- something the Greens may lack the organisational power to do.
The Greens could however play a key role by chipping away at Labour support in key constituencies, with the left-leaning party neck-and-neck against Prime Minister David Cameron's centre-right Conservatives.
Bennett told AFP she would not join a coalition with either party, but would consider supporting Labour "on a vote-by-vote basis".
The Greens' priority demands in any negotiations would be a reversal of austerity and the scrapping of Britain's Trident nuclear weapons programme, she added.
University of Manchester senior politics lecturer Robert Ford said the main impact of the Greens would be its effect on Labour, which is also facing pressure from the Scottish National Party and the anti-European Union UK Independence Party.
"It's such a close election that every one of these things count. If five seats tilt away from Labour because of the Greens that's a big problem for Labour," Ford said.
London conservation worker Cia Marsh, 25, said she was inspired to join the Green Party following mass political engagement in the Scottish referendum in September, in which an 85 percent turnout broke British records.
"As a young person I'm very aware the government is failing me and that none of the other parties have any interest in my generation," Marsh told AFP.
The party enjoyed a blaze of publicity after their exclusion from TV election debates between party leaders caused an extended political row.
Broadcasters are now planning to include the Greens in a seven-party debate -- but the increased media scrutiny has come with risks.
The party has been forced on the defensive over policies such as a basic "citizen's income" critics said was unworkable and the decriminalisation of membership of terror groups including the Islamic State.
Nevertheless, Green policies are the most popular in Britain according to the Vote for Policies website, which tests users on what policies they agree with, without revealing what party manifesto they come from.
But the party faces a challenge in coping with an influx of new members, who bring money and manpower, but lack political experience.
Its only current lawmaker, former leader Caroline Lucas, faces a tough re-election battle in the coastal town of Brighton, damaged by the Green town council's struggle to manage internal disputes and industrial action over bin collection.
Meanwhile, Bennett's London campaign has no shortage of newly signed-up volunteers.
"This is the only party that is against austerity," said doctor Paul O'Brien, 63. "People have given up on Labour, they are a hopeless party in the sense that there's no hope."
O'Brien said he began handing out leaflets for the Greens in recent months due to concern for the strained National Health Service -- an issue that has emerged a centrepiece of the election campaign.
"I've seen the impact of relentless cost cutting that is weakening, damaging and demoralising the health service, and we have to change that."
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