Theresa May has refused to commit to acting “now” to end the UK’s net greenhouse gas emissions by 2050 – as demanded by her climate change advisers – drawing fire from environmental groups.

Campaigners voiced alarm after the prime minister said only that she will “respond urgently” to the call for new laws – pointing to the need to examine a “long and detailed” report first.

The comments fell far short of the call by the Committee on Climate Change (CCC) to enact immediately a legally binding duty to hit the 2050 target, ahead of a UN summit in September.

Greenpeace warned the prime minister of a public backlash if ministers “think they can keep their heads down and wait for this to blow over”, while Friends of the Earth urged her to “stop dithering”.

And Bright Blue, a liberal Conservative think tank, urged Ms May to “do something uncharacteristically bold” by making the legal commitment before she quits No 10.

John Gummer, the CCC’s chairman, had called for the zero-emissions target for 2050 to be made law immediately, saying: “We must do it now. The urgency is not just a matter of a shortness of time – the quicker you do it the cheaper it is.”

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Quizzed about the report, Ms May’s spokesperson said it “sets us on a path to be the first major economy to legislate to end our contribution to global warming entirely”.

But asked, by The Independent, if the prime minister would act immediately, they said: “The report is 300 pages long – it contains a lot of detailed analysis and recommendations

“We will be responding urgently to those, but we do need to give those proper considerations.”

Pressed again on the call to act without delay, the spokesperson added: “We welcome the report, but we do need to look at its recommendations, because it is a very long and detailed and thorough report.”

The comments follow growing criticism that the Brexit crisis has left a “zombie government” without the bandwidth to respond to other challenges.

In the most notorious example, it is four months since the health secretary, Matt Hancock, pledged that plans to end the social care crisis would be published “soon” – but they have yet to appear.

Dr Doug Parr, Greenpeace UK’s chief scientist, said: “We’re in a climate emergency, so the government needs to commit to legislate on this as soon as possible.

“The important thing is to set out political ambition straight away. If the government think they can keep their heads down and wait for this to blow over they’ve not been paying attention.”

The CCC blueprint would mean the end of petrol and diesel cars and gas boilers, a drastic cut in people’s meat consumption, and the planting of at least 1.5 billion trees.

The target is for net zero emissions because greenhouse gases from some activities, including air travel and farming, will remain unavoidable by 2050.

These would be balanced by taking carbon out of the air by growing trees or burying carbon dioxide below ground level.