Britain has given the go-ahead to develop the UK’s biggest untapped oilfield off Shetland, sparking outrage from environmental campaigners. The UK oil and gas regulator’s decision to grant the Oslo-listed Equinor and the British firm Ithaca Energy permission to develop the Rosebank oil and gas field in the North Sea was condemned by the Green party MP Caroline Lucas as “the greatest act of environmental vandalism in my lifetime”. “We have today approved the Rosebank field development plan, which allows the owners to proceed with their project,” the North Sea Transition Authority said in a statement on Wednesday. “The FDP is awarded in accordance with our published guidance and taking net zero considerations into account throughout the project’s lifecycle.” The field has the potential to produce 500m barrels of oil in its lifetime, which when burned would emit as much carbon dioxide as running 56 coal-fired power stations for a year. Green campaigners, including Greta Thunberg, had called on the UK government to halt the development, arguing that it contravened Britain’s plan for a net zero economy. “Rishi Sunak has proven once and for all that he puts the profits of oil companies above everyday people,” said Philip Evans, a Greenpeace UK climate campaigner. “We know that relying on fossil fuels is terrible for our energy security, the cost of living, and the climate.” Rosebank could produce 69,000 barrels of oil a day – about 8% of the UK’s projected daily output between 2026 and 2030 – and could also produce 44m cubic feet of gas every day, according to Equinor. Tessa Khan, a climate lawyer and the executive director of the campaign group Uplift, which helped coordinate the Stop Rosebank campaign, said a legal challenge could be mounted against the government. “There are strong grounds to believe that the way this government has come to this decision is unlawful and we will see them in court if so,” she said. Hannah Martin, a co-director of Green New Deal Rising, said: “Approving the Rosebank oilfield is an act of climate vandalism by Rishi Sunak and his government … but Labour has not committed to reversing this decision, despite acknowledging that Rosebank’s approval is wrong. “This position does not make sense, and there is still time for Keir Starmer to put himself on the right side of history and show leadership by committing to revoking Rosebank’s licence.” Members of Fossil Free London and Stop Rosebank protested outside the Department for Energy Security and Net Zero on Whitehall Place. Starmer defended Labour’s position on the Political Thinking with Nick Robinson podcast on Thursday. “What we’ve said is no new licences to be granted when we’re in power, but we won’t revoke anything, any licences that are granted before we come into power,” he said. “I’m mindful of the fact that if there’s one thing that has killed growth in the last 13 years – and it has been killed – it’s the chopping and changing lack of strategic thinking. And therefore, as a matter of principle, we will accept, as it were, the baseline that we inherit from the government if we win that election.” Simon Francis, the coordinator of the End Fuel Poverty Coalition, said: “Hidden in the small print of the deal is that this project can only go ahead thanks to a massive tax break the government is giving to international oil and gas giant Equinor. “Households struggling with their energy bills will be shocked that the new energy secretary has chosen to hand a multibillion-pound tax break to this Norwegian firm … Figures show that more North Sea production will only give us an extra year of domestic gas, which will be charged to struggling households at global market prices.” Claire Coutinho, the secretary of state for energy security and net zero, said the UK needed to “be pragmatic”, with oil and gas forecast to still be needed for a quarter of the country’s energy needs in 2050. “We will not play politics with our energy security,” she posted on X. “The choice we face is this: do we shut down our own oil and gas leaving us reliant on foreign regimes? Do we lose 200,000 jobs across the UK? Do we import fuel with much higher carbon footprints instead? And lose billions in tax revenue? “We are a world leader at reducing carbon emissions but as much as we will be ambitious, we must be pragmatic.” The chancellor, Jeremy Hunt, said: “We are accelerating renewables and nuclear power but will still need oil and gas for decades to come – so let’s get more of what we need from within British waters.” Permission to develop the field has come a week after Sunak announced a U-turn on the government’s climate commitments, including pushing back the deadline for selling new petrol and diesel cars and the phasing out of gas boilers. The Rosebank project has faced stiff resistance, with hundreds of climate scientists and academics and more than 200 organisations, from the Women’s Institute to Oxfam, joining tens of thousands of people across the UK in opposing it. The International Energy Agency warned before the UK-hosted Cop26 climate summit in 2021 that no new oil and gas exploration should take place if the world was to limit global heating to 1.5C above pre-industrial temperatures. This year, the UN secretary general, António Guterres, called on governments to halt new licences for oil and gas exploration and development.