The Conservatives’ former net zero tsar has revealed that he intends to vote Labour for the first time because Rishi Sunak has been “siding with climate deniers” to politicise the energy transition. Writing exclusively in the Guardian, Chris Skidmore, a former energy minister, said he could not back the Tories, who had argued that net zero was “a burden and not a benefit”, a decision that he said would cost it votes. In a deeply personal attack, he accused the prime minister of breaking the consensus of the past on climate action to “seek division and polarisation”, suggesting it was the “greatest tragedy” of his premiership. “Worse still has been the rhetoric and extreme tone that has sought to politicise net zero as being forced upon people, a false narrative that is either the product of ignorance, or deliberate misinformation,” he said. The former Tory MP, who attended cabinet in his previous role, becomes the most senior figure yet to switch his support to Labour, after a small handful of Tory backbench defections, in a further blow to Sunak’s campaign. The prime minister has had yet another difficult week, with four polls suggesting the Tories were on track to suffer their worst ever defeat and senior cabinet ministers projected to lose their seats. The polls, combined with warnings from Tory figures that Labour would have unchecked power if it won a large majority, have raised suspicions that the party is now engaged in damage limitation rather than trying to win. Sunak was preparing for a showdown with the public at the BBC’s Question Time Special on Thursday night, which was also set to feature Keir Starmer, Ed Davey and SNP leader John Swinney on the panel. He has become mired in a row over alleged betting on the general election date after it emerged that a second Conservative candidate and the party’s campaigns director were being looked into by the Gambling Commission. The watchdog is examining bets allegedly placed by Laura Saunders, the Tory candidate in Bristol North West, and her husband, Tony Lee, who is now on leave of absence from his job at party headquarters. Last week the Guardian revealed that the prime minister’s closest parliamentary aide, Craig Williams, placed a £100 bet with Ladbrokes on a July poll, three days before Sunak announced the date. Sunak has been widely criticised for allowing new oil and gas licences, doing too little to improve the condition of the UK’s rivers and beaches, which are filthy with raw sewage, and, while vowing to stick to net zero, dismantling many of the policies – on electric vehicles, boilers, public transport – needed to get there. Skidmore, who resigned as a Tory MP in January in protest at the party’s dash for oil and gas, triggering a byelection in his Kingswood seat that Labour won, had been a leading voice within the Tory party on green issues. He was the energy minister who signed into law the former prime minister Theresa May’s “net zero by 2050” pledge. More recently, he led the government’s net zero review, which was published in September 2022. In his piece for the Guardian, he criticised Sunak’s decisions to prioritise new oil and gas licences, scale back measures that would have saved households billions in energy bills and “pass on” the huge economic opportunities of transition. But his sharpest criticism was reserved for what he suggested were the prime minister’s attempts to transform net zero into a culture war issue in a bid to draw dividing lines with the Labour party before the election. “No one is in the pay of Just Stop Oil or Putin. No one has ever been told they must remove their boilers, or replace their petrol cars, for the energy transition is just that: a moderate transition from the past towards the future.” Skidmore said previous Tory governments had understood that change would be required to reach net-zero climate targets and needed to be carefully managed and incentivised. “Rishi Sunak’s decision instead to side with climate deniers and to deliberately politicise the energy transition, breaking the consensus of the past to seek division and polarisation, is perhaps the greatest tragedy of his premiership,” he said. “It has cost the UK not just environmentally, but economically, and it has cost the Conservative party the ability to demonstrate that it is the party of the environment and nature. “It is a decision that will cost votes, including my own. For the first time, I cannot vote for my party that has boasted of new oil and gas licences in its manifesto, or that now argues that net zero is a burden and not a benefit.” The former Conservative, who is now a professor, said he would now transfer his vote to Labour, which has pledged to deliver a “green industrial revolution” to meet net zero targets. Keir Starmer’s party has also faced criticism for cutting its £28bn green investment plans by half, infuriating environmental campaigners, who said it would push up costs in the long term and make it harder for Labour to reach ambitious green targets. However, Skidmore said: “Like many others who know that we have no choice, nor any more time, but to tackle the climate crisis now, I have decided that the Labour party is best placed to achieve [that]. For this reason, I will be voting Labour at this election. ”It is a decision that I know others have and will be making also … All Conservatives serious about delivering real change to reduce emissions and grow our economy should be thinking the same.” The shadow energy and climate secretary, Ed Miliband, said: “This endorsement shows that only Labour has the practical and ambitious plan needed to secure Britain’s energy supply, end the cost of living crisis, and grow our economy by investing in clean homegrown power for our country. “As even former Conservative ministers are now making clear, voters face a stark choice at this election: between a Conservative party that would leave our climate and our economy exposed, and a Labour party with a clear plan to grow our economy, make us energy-independent, cut bills for good, and tackle the climate crisis. “Labour’s plans, starting with Great British Energy, will make our country better off by cutting bills for families and seizing the industrial opportunities of net zero, bringing good jobs to our communities.”