Rishi Sunak's government has delayed legally binding targets aimed at curbing pollution and restoring nature.
The government said its 31 October deadline for setting targets to improve water, air and wildlife would be missed.
MPs and green groups said failing to hit the deadline ahead of the COP27 climate summit was embarrassing for the UK.
The delay comes as the prime minister faces criticism for skipping COP27.
Political opponents and environmental campaigners have accused Mr Sunak of a "failure of leadership" for deciding not to attend the conference in Egypt next month.
But Mr Sunak has defended his decision, insisting that while tackling climate change was "important" to him, he was focused on domestic challenges.
The delay of environmental targets raises further questions about Mr Sunak's commitment to green goals as his government grapples with economic turmoil at home.
The government had planned for the targets to be ready before the COP27 summit, where the UK's delegation would have been able to present them to other nations.
Passed in November last year, the Environment Act requires that at least one target is set in each of four priority areas: air, water, biodiversity, and waste reduction.
But in a statement to MPs, Environment Secretary Therese Coffey said the government would not be able to publish the targets by 31 October, "as required" by law.
Ms Coffey cited the "significant public response" to a government consultation on the targets as the reason for the delay.
She said the government received over 180,000 responses to the consultation, which asked for public feedback on its target proposals and closed on 27 June.
Those responses "needed to be analysed and carefully considered", Ms Coffey said, but gave no new date for the publication of the targets.
She said the government would "continue to work at pace" to publish the targets and bring them before Parliament, where they will need to be approved to come into force.
Katie-jo Luxton, RSPB England's director of global conservation, said the delay left "a huge question mark over when we can expect to see the final targets".
She said the targets would reassure the the public, "who are rightly concerned that almost half of England's wildlife is in decline and more than one in 10 species is threatened with extinction".
In a tweet, Green Party MP Caroline Lucas wrote: "Defra admits in a cursory statement slipped out this morning that it's failed to fulfil statutory duty to publish environment bill targets. This matters."
Labour's shadow environment secretary, Jim McMahon, described the failure to meet the deadline as "a huge embarrassment to them and deeply worrying for the UK's environment".
"This is yet another example of the Conservatives being all talk when it comes to the environment, but failing to provide the leadership and the action that is desperately needed," he said.
Using the hashtag "AttackOnNature", RSPB England shared a video on Twitter of Ms Lucas asking the prime minister about Liz Truss's government having taken a "wrecking ball to nature".
Lord Lucas, a hereditary member of the House of Lords, responded with a foul-mouthed swipe at the wildlife charity.
"You lying turds. There is no attack on nature, there never was an attack on nature, and that is what Rishi confirms," tweeted the Conservative peer.
The news that Mr Sunak will not be attending COP27 comes as a UN report warns there is "no credible pathway" to keep the rise in global temperatures below a key threshold of 1.5C.
Scientists believe that going beyond 1.5C would see dangerous impacts for people all over the world.
On Wednesday, United Nations secretary general AntÃ³nio Guterres told the BBC countries must reprioritise climate change or face catastrophe.
Meanwhile, No 10 have confirmed Climate Minister Graham Stuart - who was reappointed to the role in Mr Sunak's reshuffle - will no longer attend cabinet,
Last month, under the Truss premiership, the government announced a review of the UK's target to achieve net zero carbon emissions by 2050.
Former Energy Minister Chris Skidmore was tasked with leading the review "with a focus on ensuring the UK's fight against climate change maximises economic growth, while increasing energy security and affordability for consumers and businesses".