The coalition is watering down a commitment to tough new environmental emissions standards, raising the possibility of dirty coal-fired power stations such as Kingsnorth going ahead.

Green groups are aghast that a flagship policy called for in opposition by both Lib Dems and Tories, and which they last year tried to force on the Labour government, will now not be implemented in the coalition's first energy bill to be published this year.

Their criticism of the government's commitment to green issues follows news last week that nature reserves could be sold off as countryside protection measures also bear the brunt of budget cuts in the Department for Environment.

Introducing a so-called "environmental performance standard" (EPS) for power companies would have restricted greenhouse gas emissions from coal and gas plants and encouraged companies wishing to build to use more efficient technology.

The introduction of an EPS was personally championed by David Cameron, George Osborne and Nick Clegg when in opposition; their opposition to Kingsnorth became something of a cause célèbre – and even features in the coalition agreement – but was opposed by energy companies and Tory backbenchers.

The chief executive at one coal-plant operating company warned that the UK's renewable energy technology – which would be used to help new plants meet the target – was too undeveloped to make the EPS feasible.

Now government sources confirm they will not be bringing forward legislation in the autumn and will instead spend the summer working on "the larger picture". They will open a consultation on the idea in the autumn with the results being presented to parliament as a white paper in the new year.

Green campaigners believe this is noncommittal for a policy both parts of the coalition said could be implemented immediately when in opposition.

They believe a delay in the introduction of the standard until next year – with a few years for the legislation to pass through the house and for it to be set up – raises the possibility of new coal-fire power stations slipping through the system.

Greenpeace energy campaigner, Joss Garman, said: "David Cameron made the introduction of new rules to stop the most polluting power stations one of his flagship green policies, and Nick Clegg helped ensure it was a key part of the coalition agreement.

"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?"

The energy company Peel Power has already come forward with a proposal in Scotland to build a largely unabated coal plant.

The government's advisers, the Committee on Climate Change, said if the UK is to meet its climate targets it needs to decarbonise the whole power sector by 2030.

If the EPS is abandoned it would almost certainly reopen the debate about what the industry needs to change and encourage utilities to push forward with their original plans for a whole new fleet of dirty coal stations in the UK (the first to be built here for 30 years).

The consequences would be that the battle of Kingsnorth could be refought.

Along with opposition to the third runway at Heathrow, introduction of the EPS to bind the construction of new power plants was a key policy for both the Tories and Lib Dems.

In 2006 Cameron first proposed the idea, pointing to the experience of California. In June 2006, he said: "I can announce today that 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.

"Such a standard would mean that a new generation of unabated coal power plants could not be built in this country." In July 2008, Osborne repeated the pledge verbatim.

When Ed Miliband's energy bill came to parliament for a vote it was Conservative and Lib Dems who worked together to amend it to enable an emissions performance standard.

Though the plan had Cameron and Clegg's support during their time in opposition, Cameron's party was not convinced. At the time, the amendment put him on a collision course with his backbenchers, who remain hugely sceptical of his green agenda, and he did not impose a three line whip on them when they voted on the proposal.