Environment Minister Zac Goldsmith has announced his resignation, accusing the government of apathy over environmental issues.
In a letter to Rishi Sunak, he accused the prime minister directly of being “simply uninterested” in climate commitments.
Mr Sunak framed the resignation as one not of principle but the consequence of Mr Goldsmith's reluctance to apologise.
The resignation letter posted on Twitter said Britain had "visibly stepped off the world stage and withdrawn our leadership on climate and nature".
Mr Goldsmith wrote: “Prime Minister, having been able to get so much done previously, I have struggled even to hold the line in recent months.
“The problem is not that the government is hostile to the environment, it is that you, our Prime Minister, are simply uninterested. That signal, or lack of it, has trickled down through Whitehall and caused a kind of paralysis.”
This week he was criticised by the Privileges Committee for remarks he made about the partygate inquiry that, in turn, led to Boris Johnson's resignation as an MP.
He was also criticised for retweeting a tweet on June 9 that called the inquiry a witch hunt and kangaroo court.
The report quotes him as saying: “Exactly this. There was only ever going to be one outcome and the evidence was totally irrelevant to it.”
He said he was horrified that key animal welfare commitments have also been abandoned, such as the Kept Animals Bill.
The Prime Minister hit back by saying Mr Goldsmith had been asked to apologise over his comments about the Privileges Committee inquiry that found Mr Johnson lied to MPs over partygate accusations.
"You were asked to apologise for your comments about the Privileges Committee as we felt they were incompatible with your position as a Minister of the Crown. You have decided to take a different course."
Labour had demanded his resignation.
Questions were raised in Parliament on Thursday over whether he could continue as a minister after the criticism of his conduct by the Privileges Committee.
Labour former minister Lord Foulkes of Cumnock said: “Lord Goldsmith is one of the subjects of this report produced by the Privileges Committee. It is an extraordinary report, the likes of which I have never seen before.
“Lord Goldsmith, a minister of the House of Lords, is severely criticised by the Privileges Committee for interfering in the procedures of the House of Commons. In my 44 years in Parliament, I have never known such a criticism. It is astounding. What is happening to Lord Goldsmith?
"Is he able, in the light of this criticism, to continue as a minister of the government?”
