Environmentalists are threatening legal action in an attempt to halt the development of a new gasfield in the North Sea that has been given the green light by the UK government. Climate experts reacted with anger after the government announced it had given the Jackdaw field, to be developed by the oil multinational Shell, “final regulatory approval” on Wednesday. The business secretary, Kwasi Kwarteng, said: “Jackdaw gasfield – originally licensed in 1970 – has today received final regulatory approval. We’re turbocharging renewables and nuclear but we are also realistic about our energy needs now. Let’s source more of the gas we need from British waters to protect energy security.” However, climate experts said the decision, announced on the eve of the long bank holiday weekend, flew in the face of clear evidence from scientists that countries had urgently to cut greenhouse gas emissions to avoid the worst effects of the climate crisis. According to a recent scientific study, nearly half of existing fossil fuel production sites need to be shut down early if global heating is to be limited to 1.5C, the internationally agreed goal for avoiding climate catastrophe. This goes beyond the call by the International Energy Agency in 2021 to stop all new oil, gas and coal developments, a statement seen as radical at the time. Ami McCarthy, a political campaigner for Greenpeace UK, said approving Jackdaw was “a desperate and destructive decision” and proved the government had no long-term plan. “They could immediately shave billions off bills, get a grip on UK energy demand, create thousands of jobs, boost our economy, tackle the climate crisis and avoid future crises – if they just upgrade homes to be warmer and greener, and invest in clean and cheap renewable power. But instead, once again, they’re handing out lucrative permits to the likes of Shell for a project that won’t start producing gas for years, that won’t lower our bills, but will create massive emissions, causing deadly flooding and wildfires.” She said Greenpeace believed the decision was unlawful and was considering legal action to stop it. “We will fight this every step of the way,” she said. The Green MP, Caroline Lucas, joined those deriding the proposal. Shell welcomed the decision on Jackdaw and said it planned to go ahead with the field’s development “at a time when UK energy security is critically required”. It said: “Responsibly produced, local gas production plays an essential role in the UK’s transition to net zero, will support thousands of jobs, and forms part of Shell UK’s broader intent to invest £20bn-£25bn in the UK, with 75% intended for low- and zero-carbon products and services.” Activists from the newly formed Stop Jackdaw campaign said they would hold protests on Thursday outside UK government offices in London and Edinburgh to demand the government reverse its decision. One Jackdaw campaigner, Lauren MacDonald, said: “This government has no idea how to solve the energy crisis. It’s still looking to oil and gas for the answer when that is precisely what is driving the cost of living and climate crises.” Jackdaw is just the latest major UK fossil fuel project to have been approved since the UK hosted the Cop26 climate conference in Glasgow last year – to the dismay of climate scientists and campaigners. Earlier this month a Guardian investigation found the world’s biggest fossil fuel firms were quietly planning 195 “carbon bombs” – huge oil and gas projects that would drive the climate past internationally agreed temperature limits with catastrophic global impacts. In April, the UN secretary general, António Guterres, gave a warning to fossil fuel corporations and governments planning new extraction projects. “Investing in new fossil fuels infrastructure is moral and economic madness,” he said. “Climate activists are sometimes depicted as dangerous radicals. But the truly dangerous radicals are the countries that are increasing the production of fossil fuels.”