Four of Britain's largest green groups challenged George Osborne last night over his slighting reference to climate change campaigners as the "environmental Taliban".
The Independent reported yesterday that the Chancellor had started using the phrase to poke fun at the green lobby within the Government and the Conservative Party. In a joint letter to Mr Osborne, Friends of the Earth, Greenpeace, the RSPB and WWF-UK said they would be "most grateful" if he could clarify his comments.
Andrew Pendelton, the head of campaigns at Friends of the Earth, said: "If he has made this comment, it is potentially deeply offensive. It is offensive to us as professionals working in these organisations, but also to the millions of people who support these organisations.
"They are campaigning on issues that are critically important – it is not a trivial matter. Do we have a Government or a Chancellor who, when he is challenged on something, thinks is a good idea to engage or throws insults around?"
John Sauven, the executive director of Greenpeace UK, said the Chancellor's comments would dismay potential investors in environment-friendly projects.
"It's part of a consistent pattern – he is quite open about his support of a 'dash for gas' and doesn't support renewables.
A spokesman for the Chancellor said: "We do not know where these reports came from. It is simply not the case that he has used these words."