Alok Sharma, who led last year’s COP26 climate conference in Glasgow, has threatened to quit if the new prime minister ditches the current commitment to reach net zero carbon emissions by 2050.

The cabinet minister said a failure to follow the policy backed by Boris Johnson would cause “incredible damage” to the UK’s international reputation.

Mr Sharma also accused some of the candidates in the Tory leadership contest of being “lukewarm” on net zero.

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“Anyone aspiring to lead our country needs to demonstrate that they take this issue incredibly seriously, that they’re willing to continue to lead and take up the mantle that Boris Johnson started off,” Mr Sharma told The Observer.

“I want to see candidates very proactively set out their support for our net zero agenda for green growth.”

Asked whether he would resign his position in the Cabinet Office, he said: “I don’t rule anything out and I don’t rule anything in.”

Only Kemi Badenoch – one of the five remaining candidates – has said she does not support reaching net zero by 2050, describing it as “unilateral economic disarmament”.

Foreign Secretary Liz Truss said on Friday that she would impose a temporary moratorium on the green levies on domestic energy bills if she became PM, arguing there were better ways to achieve the net zero target.

Former Conservative leader Sir Iain Duncan Smith, who is backing Ms Truss, told Sky News some of those levies should be reconsidered.

He said the rising cost of living – which he described as the “number one crisis” – meant net zero may need to be put on the “back burner whilst we make sure people don’t suffer”.

He added: “We have the capacity to reduce the burden on them by getting rid of some of these green levies.

“Yes we want to get to net zero, but we need to do it in a way that we don’t crush the public while we’re doing it.”

Another candidate, Penny Mordaunt, tweeted in January: “There is a path to net zero which makes economic sense and ensures our resilience.”

Rishi Sunak has signed up to the Conservative environment pledge, which includes “unleashing clean British energy” and “backing the technologies of the future”.

Tom Tugendhat told The Telegraph he would “keep the (net zero) target”.

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