Labour must combine tackling the climate crisis with pursuing social justice, if elected, to show that achieving net zero will not be done “on the backs of the poor”, the UK’s outgoing Green party MP has warned. Caroline Lucas, who has held the seat of Brighton Pavilion since 2010, said: “The biggest priority is to demonstrate that is not the case. We have to make sure that this is a strategy and a policy that is the opposite of being done on the backs of the poor.” That should be achievable, she added, as social justice and shifting to a green economy go hand in hand. But if Labour takes power, as polls predict, the party must avoid mistakes that put costs on low-income families or that hurt people’s jobs, she said. “The truth of it is that the policies that we need to get [greenhouse gas] emissions down are actually policies that will increase people’s wellbeing in any case,” she said. Home insulation was one example, where if a minimum energy efficiency standard were enforced on landlords then tenants would have warmer homes, less energy waste and lower emissions. “Again and again there are concrete examples of where green policy is actually social justice policy, it’s one and the same thing. But that story doesn’t get told nearly strongly enough.” Lucas looked beyond the current election to the next, five years away, to warn that a resurgent Conservative or Reform party right wing would be planning to “weaponise” the climate crisis, and would seize on any missteps by Labour on the issue. “There’s a lot of hope riding on what a new Labour government could do after 14 years of Tory chaos, and if they aren’t seen to deliver something in that first term then I worry about what’s going to happen during those next four or five years is that [Nigel] Farage and [Kemi] Badenoch and whoever else within the Tory right are going to be reorganising and getting ready for a comeback. And surely one of the things they’re going to have on top of their list is going to be rolling back on net zero still further,” she told the Guardian. Lucas warned that Labour was not putting enough money behind net zero to ensure that its ambition for a “just transition” to a green economy could be met. Earlier this year, Keir Starmer scaled back a longstanding pledge to invest £28bn a year in a “green prosperity plan”, roughly halving the money available, even though economists and industrial experts forecast that the original investment would be quickly paid back by supercharging economic growth. “If there isn’t enough money on the table – for example, if there isn’t a sufficiently well-resourced scrappage scheme [for people moving away from diesel cars] – it’s easier for people to make the case that this policy is going to hurt those on lowest incomes,” she said. “Unless Labour is willing to get out of the straitjacket it has voluntarily and arbitrarily strapped itself into [on spending] then net zero will be one of those areas of policy that they’re not going to be able to deliver on during their first term, and therefore the level of disillusionment, disengagement, disappointment is going to ratchet up.” The Green party is planning to put candidates in all constituencies across the country, but targeting four key seats to win, as the first past the post system militates against them. Polling suggests the party could win two rural seats, while national polls, which usually downplay Green support, indicate they are likely to retain Lucas’s old seat of Brighton Pavilion and gain Bristol Central, a constituency newly created by boundary changes. Lucas is enthusiastic about the impact of this potential quadrupling of Green MPs. “The thing that I found most stressful about being a Green MP over the past 14 years has been the fact that I can’t be in more than one place at once,” she said. “All the time there is so much to be done, and [so] the idea that the four of us at least could spread our voice and amplify our voice across so many more places at any given time within the parliamentary day is just so exciting. “One of the things we always say is that a Green in the room changes the nature of the debate because questions that wouldn’t otherwise be asked are being asked.” Lucas still strongly advocates a change to the UK’s voting system to a form of proportional representation, as the Green party has never achieved more than a single seat in parliament despite having polled 866,000 votes at the last election. She dismissed fears that the Reform party, led by Farage, which has anti-net zero policies and whose chair, Richard Tice, has made many false statements about climate breakdown and net zero, would benefit from changing the system. “I don’t think you should skew your democratic system for fear of what it throws up. I am absolutely no fan of Nigel Farage, his politics are abhorrent to me, but I would far rather we address the symptoms that have given rise to his popularity, rather than trying to suppress things we don’t like,” she said. “We should have a fair voting system because that’s the democratically right thing to do.” Sian Berry will contest Lucas’s old seat in Brighton. Lucas is leaving to become an end of life doula.