Outside the open air market on Brighton's London Road, the Green Party leader Caroline Lucas is doggedly trying to convince late afternoon shoppers that her party is a serious choice in the May elections. "I want to give Labour a bit of a kicking," confides a man in his forties. "Well, take the clothes peg off your nose and vote for us," says Lucas, breezily. "We're the bookies' favourites."
She may have a point. Thanks in part to the widespread disillusionment with mainstream politics, this year could see the Greens, who are standing over 300 candidates nationally, win their first Westminster seat. The party is making headway in the former Home Secretary Charles Clarke's seat of Norwich South, and in the London constituency of Lewisham Deptford, but Brighton Pavilion, where Lucas herself is standing, remains their best chance. In December, an ICM poll of voters in Brighton Pavilion, put the Greens in the lead, at 35 per cent.
To some this might come as a surprise - now that the environment is firmly on the agenda of all three main parties, haven't the Greens lost their unique selling point? Yesterday both Labour and the Lib Dems set out their "eco manifestos", the message of the Lib Dem leader Nick Clegg being: "don't give your vote to a Green Party that cannot make a difference in Westminster."
The Greens responded angrily, branding Clegg's party "eco-charlatans". And when we speak, Lucas is scathing about her various rivals. "They're not actually delivering on their promises. If you want green policies you have to have to come to the Green Party to get them."
But the Greens are also hoping to attract voters - in particular, disgruntled Labour supporters - with an unashamedly left-wing manifesto, which promises to tax the rich, raise the minimum wage, provide free care for the elderly and invest massively in public transport. For Lucas, these elements are intimately linked with environmental issues. "We want to radically change the way we produce and consume. We're now the party of social justice - after 13 years it's a scandal Labour hasn't done more."
This direction is in no small part due to Lucas, an engaging and intelligent MEP who became the Green Party's first leader in 2008. (Until that point the party had operated without a formal leader, instead electing "principal speakers" - egalitarian enough, but one not perhaps best suited for the cut and thrust of modern politics.) Lucas raised eyebrows in Labour circles when she was invited to speak at the conference of the Labour pressure group Compass last summer, and again at a Compass event at the September Labour conference.
It was a move that prompted one Labour blogger to declare: "We don't need a dialogue with these single-issue clowns and their anti-working class policies, we need to attack and destroy them." But with talk of a hung parliament and coalition building rife - not to mention Labour's dismal third place in the opinion polls - this tribalism seems a little outdated.
So, in a dream scenario for the Greens, a newly-elected Lucas holds the balance of power in Parliament. Which way would she turn? Her response is guarded: "we would be supporting proposals on a case by case basis, not going into a formal coalition."
Presumably, then, Lucas could envisage voting alongside the Conservatives in some cases? "In the unlikely event that the Tories come up with some proposals that we could support, yes. For example they were against the Heathrow airport expansion so Greens on the London Assembly supported them there."
That seems like a tricky strategy for a party that pledges a commitment to social justice. "Our direction of travel is very much on the left," says Lucas. We would be likely to support measures that would promote our aims of a fairer, greener Britain. Addressing inequality through [economic] growth and accumulating more and more stuff on a planet of finite resources isn't going to be sustainable into the future. Therefore the role of redistribution is even more important to the Green agenda."
First, though, the Greens actually have to win a seat. They polled more than a million votes in last year's European elections and Lucas is optimistic about her chances in Brighton. The Greens have always done well among Brighton's alternative-minded middle class - they hold 13 seats on the local council, largely elected by affluent wards in the city centre - but Lucas needs to broaden her support. That's why, today, she has set up stall outside the market on London road, one of the highways that stretch away from Brighton's quaint seafront into the city's poorer outskirts.
Despite its location in the South East, Britain's richest region, and its attractiveness as a home for commuters who work in London, Brighton has high unemployment and a 2008 NHS report found that deprivation had contributed to poorer health than than the national average among its population of 250,000. Aren't there occasions when green politics would come into conflict with the more immediate needs of Brighton's working class constituents? What, say, if a major car manufacturer offered to build a plant locally, promising thousands of jobs?
"Then we'd work with them to make that the greenest car company ever," says Lucas. "Job creation is massively important to us and that's why we've suggested one way of tackling the economic crisis is a massive investment in renewable energies. Not only because it's a way of getting our emissions down but also because it's a quick and effective way of getting people back to work."
Lucas challenges the old prejudice that environmentalism is a middle-class luxury. "When I appeared on Question Time [in March], I was challenged for supporting the British Airways strikers and they were saying 'why on earth are you supporting workers in the aviation industry?' Well, it's true we don't want the aviation industry to go on growing, but you can't do it by using the most harsh and unreasonable conditions to throw people out of work. We'd want to work with and retrain people in order to shift to a more sustainable economy."
Given that all three main parties, whichever one comes out on top after 6 May, have committed themselves to drastic spending cuts, having voices like those of Lucas in the mix might just make Britain a more bearable place to live over the years to come.