Former environment secretary John Gummer has attacked Chancellor George Osborne for proposing an "illegal" approach to cutting the UK's carbon emissions.
The Tory peer, who sits in the House of Lords as Lord Deben, said the Government is allowing people to cast doubt on its "fundamental support" for environmentally-friendly policies.
His comments follow Mr Osborne's claim in his speech to the Conservative Party conference this month that a decade of environmental laws and regulations are "piling costs on the energy bills of households and companies".
The Chancellor added: "We're not going to save the planet by putting our country out of business. So let's at the very least resolve that we're going to cut our carbon emissions no slower but also no faster than our fellow countries in Europe."
Debating sustainable development during the report stage of the Localism Bill in the House of Lords, Lord Deben said: "It doesn't help when the Government says things for convenience which suggest that it doesn't have its heart where it ought to be.
"It doesn't help when the Chancellor of the Exchequer suggests we are going to move at a slower speed in dealing with our emissions than the law says we have to. Proposing something that is actually illegal."
The UK is committed by law to a cut in greenhouse gas emissions of 80% from 1990 levels by 2050 and of 50% by 2025.