Rishi Sunak has given up Britain’s reputation as a world leader in the fight against the climate crisis and has “set us back” by failing to prioritise the issue in the way his predecessors in No 10 did, the government’s green adviser has warned. Chris Stark, the outgoing head of the Climate Change Committee (CCC), said that the prime minister had “clearly not” championed the issue following a high-profile speech last year in which he made a significant U-turn on the government’s climate commitments. The criticism comes after Sunak was accused of trying to avoid scrutiny of Britain’s climate policies by failing to appoint a new chair of the CCC. Sunak announced last autumn that he was moving back the ban on the sale of new petrol and diesel cars by five years, as part of a wider dilution of climate policies. At the time, the Tories were aiming to create a dividing line with Labour after their victory in the Uxbridge byelection, which largely came as a result of their opposition to London’s ultra low emission zone. “It was presented to the country as a step back from going too fast on this transition,” Stark told the BBC. “In the speech itself, he talked a lot about the need to reappraise lots of the steps that take us to net zero. I think it set us back. I think we have moved from a position where we were really at the forefront, pushing ahead as quickly as we could on something that I believe to be fundamental to the UK economy, fundamentally beneficial to the people living in this country, whether you care about the climate or not.” Stark said significant progress had been made towards net zero and praised Theresa May and Boris Johnson for their commitment to the target. However, he said Sunak had failed to show the same ambition. “We are now in a position where we’re actually trying to recover ground,” he said. “The diplomatic impact of that has been immense. It doesn’t matter that there were detailed policies within that speech that you could say were very much in line with net zero. The overall message that other parts of the world took from it is that the UK is less ambitious on climate than it once was, and that is extremely hard to recover.” A government spokesperson said: “We are the first major economy to halve greenhouse gas emissions since 1990 and have set into law one of the most ambitious 2035 climate change targets of any major economy. But we need to reach our net zero goals in a sustainable way.”