A Conservative peer and close ally of Boris Johnson has hinted he could be “very tempted” to back Labour and questioned Rishi Sunak’s commitment to tackling the climate crisis. Zac Goldsmith, the former climate minister, raised concerns at the drive in some quarters of the Conservative party to re-examine achieving “net zero” because of the potential extra cost to consumers at a time of stretched household budgets. Five weeks after leaving the government in frustration at Sunak’s “apathy” towards environmental issues, Goldsmith said he was “desperately hoping the Conservative party comes to its senses”. Concerns among environmentally minded Conservatives have increased in the aftermath of the Uxbridge and South Ruislip byelection, which the Tories claimed they narrowly clung on to because of opposition to the extension of London’s clean air zone. In the weeks after, Sunak announced more than 100 drilling licences in the North Sea to “max out” oil and gas reserves, a review into low-traffic neighbourhoods, and defended his continued use of a private jet. Goldsmith said his party did not have “a clear answer” to what he called the “biggest challenge we’ve ever faced”. “The simple truth is there is no pathway to net zero and there’s no solution to climate change that does not involve nature, massive efforts to protect and restore the natural world,” he told the BBC’s HARDtalk programme. He said he was not currently “hearing any of that from the Labour party”, but suggested he could be persuaded to back it. Goldsmith added: “If there’s a real commitment now, the kind of commitment frankly that we saw when Boris Johnson was the leader, then I’d be very tempted to throw my weight behind that party and support them in any way I could.” Labour sources indicated they thought it was unlikely Goldsmith would ever try to switch his party allegiance in the House of Lords. They also pointed to his London mayoral campaign against Labour’s Sadiq Khan in 2016, which critics said relied on dog-whistle racism, to suggest he would probably not be accepted into the party anyway. Goldsmith raised particular concerns about suggestions the government could miss its commitment to spend £11.6bn over five years on international climate schemes in developing countries. Official warnings have reportedly been made within Whitehall that an already “stretching target” had been turned “into a huge challenge” given underspending in the run up to the 2026 deadline. Goldsmith, who is a close friend of Johnson, said: “It’s great that the government is saying that they’re committed to 11.6, but mathematically, it is impossible for us to meet that target. Unless the Treasury intervenes, unless the prime minister intervenes, it’s simply impossible. “If you look at the trajectory of expenditure, in order to fulfil that promise the first year of the next government, which may or may not be this government – it might be the Labour party – will have to spend over 80% of all of its bilateral aid on climate finance and that it obviously is not going to happen.” Goldsmith has not held his tongue since quitting the government at the end of June. Speaking to the Guardian last month, he criticised several cabinet ministers and accused Sunak of “talking to a particular gallery” of climate-sceptic MPs. The prime minister has so far remained committed to the net zero by 2050 target, and resisted calls from some Tory MPs for the 2030 ban on new petrol cars to be delayed. He announced funding for carbon capture projects on a visit to Scotland last week. Though Sunak said net zero should be achieved in a “proportionate and pragmatic way”, he also said it was important to leave the environment in “a better state than we found it in”.