An unlikely revolution is being plotted over coffee and chocolate cake in the garden flat of a genteel Georgian terrace.

The insurgents’ audacious mission is to raise the Green flag in May over a slice of Bristol that has variously been in Tory, Labour and Liberal Democrat hands in the last two decades.

Until very recently their optimism would have seemed ludicrous: the Green Party lost its deposit in Bristol West at the last general election, scraping together a miserable 3.8 per cent of the vote. Now winning the constituency from the Lib Dems has become the buoyant party’s second-biggest priority – after holding on to Caroline Lucas’s Brighton Pavilion seat – in six months’ time.

It will not be easy as Darren Hall, its candidate, warns the small gathering of party enthusiasts, who are joined by a handful of wavering voters at the coffee morning. “It’s a tough gig. We are going to have to work really hard. The other parties are going to be gunning for us every day between now and the election,” he says.

In a taste of the attacks to come, Nick Clegg lambasted the Greens yesterday for being one of the parties which “espouses the politics of grievance, blame and anti-everything” and for enjoying the luxury of ducking the “big decisions” on the economy which the Lib Dems had to take in office. But Mr Hall and his party have two strong reasons for believing their “green surge” could sweep the seat into their control.

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

First, the constituency fits the demographic of areas considered receptive to Green messages. Like Ms Lucas’s power base, it has a large student population, high numbers of well-educated young professionals and a slightly raffish ambience as well as pockets of deprivation. “It is a value-driven place,” Mr Hall says. “People here were incredibly angry about Iraq, and Blair’s decision to go to war despite the views of voters and that is still very visceral for them. They then voted for the Lib Dems in the belief they were their kind of people, and now feel incredibly let down.”

Bristol also boasts a strong streak of environmentalism, electing an independent but green-minded mayor and being selected as Europe’s green capital for 2015.

Secondly, Lib Dem support in the area has faded rapidly since the party entered the Coalition. It has lost eight of its 16 councillors in four years and finished third in city hall elections in the constituency in May. The momentum is with the Greens, who collected the most council votes then, but Mr Hall warns: “It’s a huge leap from local votes to national votes.”

The sitting MP, Stephen Williams, who is also a junior minister, has built up a 10,000-plus majority and is widely praised as hard-working and popular, but Lib Dem sources acknowledge he has a fight on his hands. One admitted: “A Green win is plausible, but they would need to throw a lot of resources at it.”

That is the challenge facing Mr Hall, a former RAF officer and civil servant, who is a recent convert to the Green cause. But he can now count on the support of 500 members in the constituency and another 200 from other parts of Bristol. In recent memory local party meetings would attract just four or five stalwarts. At the coffee morning, Mr Hall wins murmurs of agreement when he tackles local concerns over parking zones and public transport and when he stresses his party’s commitment to boosting renewable energy and tackling climate change. But he runs into trickier territory when a woman tells him his party’s support for rail nationalisation “sends shivers down my spine” because of her memories of British Rail in the 1970s.

And he is temporarily ruffled by a challenge over how to tackle Britain’s mountainous deficit, replying that it is “an incredibly complicated issue” which needs a “whole set of new ideas that aren’t just fiddling”.

After wrapping up the meeting, Mr Hall heads off to an event that could not have taken place until recently – a meeting of the city’s six Green councillors, five of whom represent wards in the west of the city.

“Those councillors give the Greens a good base for their campaign,” said Lisa Harrision, a political scientist at the University of the West of England. “They have probably learnt from the tactics of the Lib Dems who have been used in the past to getting together a core group of activists.”

But Dr Harrison concluded that achieving victory in Bristol West would be a tough challenge for the party, particularly in light of the sitting MP’s high local profile.