He said the government will consult on the EPS in the autumn.

Before the elections, in June 2006, David Cameron said: "A Conservative government will follow the Californian model, and implement an Emissions Performance Standard.

"This would mean the carbon emissions rate of all electricity generated in our country cannot be any higher than that generated in a modern gas plant... and that a new generation of unabated coal power plants could not be built in this country." In July 2008, Osborne repeated the pledge.

On Monday, Huhne claimed that "It would be impossible for any new coal power station to be built without being equipped with carbon capture and storage (CCS)."

"While the details of an Emissions Performance Standard are still being finalized, we are clear that without CCS it would be impossible to meet such a standard."

He was speaking in response to criticism that the government was dragging its feet; and that the emissions limit to be set might instead be at a level that encourages the building of more gas power plants.

These plants emit between a half and a third of the carbon of non-CCS coal plants, but building more of them now would make the target of an 80 per cent carbon reduction by 2050 more difficult.

In June's Annual Energy Statement, the government said the EPS would be part of the Electricity Market Reform consultation in the autumn with a white paper in the following spring.

Greenpeace energy campaigner Joss Garman said: "Both Lib Dem and Conservative MPs voted for the introduction of such a measure just a few months ago, and if they U-turn on this and fail to put this measure into their new energy law, how can they claim to be the greenest government ever?"

A report published on Monday by consultancy Arthur D. Little also questioned whether the government's Annual Energy Statement was achievable, suggesting that targets to cut carbon by 34% by 2020 should be pushed back to 2023 to ensure there was enough time to plan a clear energy policy.