The group - which included Friends of the Earth, the New Economics Foundation, Greenpeace and the Renewable Energy Association - wrote to the prime minister, saying that it would be "unfortunate if the leadership shown by the UK in getting these European targets adopted in March were now eroded by a serious lack of ambition in our domestic policy".
"Our European colleagues will be looking to the UK to propose a realistic contribution, especially as we have the EU's best resource of wind, tidal and wave energy," the letter, seen and reported on by the Guardian, continues.
"Such lowly domestic ambition also threatens to undermine the credibility of the new climate change bill, which puts into statute the commitment to long-term emission reductions."
Downing Street has admitted that the targets are "ambitious" and says that it will be a "major challenge" to meet them.
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