Lord Zac Goldsmith, a prominent voice on environmental issues in Boris Johnson’s cabinet, warned this week that the Conservatives would be “digging our electoral grave” if they elected a new leader that was prepared to abandon the UK’s net zero carbon emissions by 2050.

Johnson, who presided over the COP26 international climate talks in Glasgow last autumn, has been a strong advocate of net zero, using every opportunity to talk up the need to switch to “clean, green energy”.

His defenestration as leader of the Conservatives has thrown into doubt the future of the governing party’s net zero 2050 target — although ripping it up would pose complicated legal and diplomatic challenges.

“Some candidates are already promising to abandon our climate and environment commitments, and others are maintaining an ominous silence,” said Goldsmith. “If we throw away the UK’s international leadership on the environment, we will lose the support of a broad coalition of voters.”

Beyond the impact on the future electability of the Tories, doubts about the party’s continued commitment to net zero has caused jitters among business leaders as any watering down of the target could have huge repercussions for medium- and long-term planning for manufacturers, energy and finance.

Half of the six candidates who made it into the second round of voting in the leadership contest on Thursday had questioned whether the UK should stick to the 2050 timetable.

Launching her leadership bid earlier this week, Kemi Badenoch, who came fourth in the second round, described net zero as a classic example of “well-meaning regulations” clogging up economic growth.

The target had been set with “no thought to the effect on industries in the poorer parts of the country”, she declared. On Thursday, she appeared to tone down her position, telling The Times: “My issue isn’t that 2050 is the right or wrong target . . . I just think we need to change how we talk about it.”

Tom Tugendhat, who also remains in the race, said he wanted to delay the net zero target, although his spokesman said afterwards he was “pro the target” but wanted “to reserve the right to flex on timescales to take into account geopolitical shocks”.

Suella Braverman, the attorney-general who was knocked out in the second round, had called for the government to “suspend the all-consuming desire to achieve net zero by 2050”, in light of the energy crisis.

Joss Garman, a director of the European Climate Foundation, said that while none of the candidates were “especially known for their green credentials” at least the front-runners — Rishi Sunak, Penny Mordaunt and Liz Truss — had pledged to stick with net zero.

Three years ago, when the House of Commons approved the 2050 target, no MP objected. But there has been growing pressure from the rightwing of British politics as the cost of living crisis mounts about the potential cost of reaching the target — for example the replacement of gas boilers with expensive electric heat pumps.

Polling has consistently found majority support from voters for the policy, however, with 60 per cent backing it in a survey in April by think-tank Onward, compared to 10 per cent who opposed it. Yet Conservative voters are less enthusiastic than others and around half would be happy to ditch the policy, the same survey found.

Both Truss and Mordaunt conceded at a hustings on Wednesday that they would be prepared to backtrack on some environmental commitments. They joined Badenoch in calling for the suspension of green levies on energy bills to help ease the cost of living crisis, echoing a call from chancellor Nadhim Zahawi, who was knocked out of the race in the first round.

Critics of the green agenda have singled out those tariffs, equivalent to about £150 a year, even though it is the rising cost of fossil fuels that is responsible for most of the eye-watering increase in energy bills.

Rolling back the UK’s climate commitments would not be simple. The UK was among the more than 190 countries to sign up to the Paris Agreement, a binding international treaty that commits nations to limiting warming to “well below” 2C. 

The UK has also codified its climate ambitions in law under the Climate Change Act, which makes the net zero 2050 goal legally binding. The legislation states any change to the headline goal may only occur if there have been “significant developments” in “scientific knowledge about climate change” or “European or international law or policy that make it appropriate to do so”. It would also need parliamentary approval.