Rishi Sunak must uphold his £11.6bn climate finance commitment, Conservative parliamentarians, including the former net zero tsar, have said. Writing to the prime minister in a cross-party letter, they say recommitting to the target and clearly demonstrating how it would be met would “avoid doing further damage to the UK’s climate leadership, and help to build a safe and more prosperous future”. Chris Skidmore, the MP who authored the government’s net zero review, is among 51 parliamentarians, including four Tories, who have written to the prime minister urging him not to let down developing countries. Caroline Lucas, the Green MP for Brighton Pavilion, who also signed the letter, told the Guardian: “The government’s commitment to £11.6bn in climate finance isn’t a ‘nice-to-have’ – it’s an absolutely critical part of the global effort to tackle the accelerating climate emergency, and a solemn promise to the international community that cannot simply be abandoned on a whim. “It must be new and additional money, too. Giving with one hand and taking with another, by diverting cash from an already depleted aid budget, won’t help those on the frontline of this crisis. Any backsliding on this commitment would leave any remaining semblance of the UK’s global climate leadership in tatters.” Sunak has drawn up plans to ditch the promise, the Guardian revealed earlier this month, after a leaked document showed officials had warned that the spending commitments to climate breakdown mitigation in the world’s most vulnerable countries were not being made. The £11.6bn is the UK’s contribution to the $100bn of climate finance from wealthy countries that was pledged in 2009 at Cop15 in Copenhagen has still not been delivered by rich nations. The UK spent £5.8bn over the previous five years up to 2021. This was doubled to£11.6bn between April 2021 and March 2026, £3bn of which was earmarked for protecting and restoring nature, meeting commitments made in Cop15 last December. This is now at risk, with civil servants revealing in a leaked briefing that it was almost impossible to meet the funding at current levels of spending. The Labour party has also refused to commit to meeting the target. “We are writing to you as a group of cross-party Parliamentarians to express our profound concern at media reports that the government is considering reneging on its commitment to spend £11.6bn on climate finance between financial years 2021-22 to 2025-26, and to urge you to uphold this vital pledge,” the letter to Sunak, delivered on Friday, reads. Skidmore, the MP Derek Thomas, Lord Randall, and Lady Hooper were the Conservatives who signed the letter, along with Labour’s Hilary Benn, and the Lib Dem net zero spokesperson Wera Hobhouse. They added that they were concerned that other parts of the Foreign Office development budget would have to be redirected as climate finance to meet the target: “We cannot take from one pot which provides lifesaving assistance to fill another, particularly where it is those least responsible for climate change who are being worst hit.”