David Cameron all but ruled out Heathrow expansion under a Tory administration yesterday, opening a rift with business and marking a significant dividing line with Gordon Brown.

The Conservative leader came down on the side of environmentalists and campaigners against a third runway, after months of internal debate.

Ministers have welcomed proposals for further expansion of Europe's busiest airport and are expected to make a policy statement this year. Business leaders have voiced their support, insisting that a bigger Heathrow will keep Britain competitive.

But Mr Cameron accused Mr Brown of using the issue as a fetish and of seeking to portray opponents as “putting lightweight environmental concerns ahead of the economy”.

“Gordon Brown is pig-headedly pursuing a third runway just to try and prove a political point,” he said in a speech on the environment and the economy. Questioning the economic value of transfer passengers using Heathrow he said that the “fiasco” of Terminal 5 had questioned BAA's ability to handle further growth.

“There are now increasing grounds to believe that the economic case for a third runway is flawed, even without addressing the environmental concerns,” Mr Cameron said, his clearest statement yet that he would block expansion if in government.

Although the formal policy remains that a Tory government would set stringent environmental tests before allowing a third runway, Mr Cameron's senior aides confirmed his speech was a “hardening of our position against Heathrow expansion”.

The change of emphasis represents a victory for Steve Hilton, his chief strategist and a strong environmentalist, over Alan Duncan, the Shadow Business Secretary, who had led those arguing the economic case for a larger Heathrow. It allowed the Tory leader to recover some support among green campaigners. John Sauven, the executive director of Greenpeace, said: “In the face of the latest climate science it would be deeply irresponsible for any government to expand the world's biggest international airport, and as Cameron said, the economics of expansion don't add up anyway.”

Mr Cameron also said that he wanted energy bills to reveal the average consumption of similar households, so that neighbourly peer pressure would ensure people tried to consume more efficiently. Each house would also have smart meters allowing homeowners to see how much energy they consumed minute by minute.

Ending the fossil-fuel culture, he said, would reduce Britain's dependence on energy supplies from countries that are often in the most volatile parts of the world and have autocratic governments. Turning to green energy supplies such as wave and tidal energy around Britain's lengthy coastline would, he said, play a vital role in reducing the carbon dioxide emissions that are driving climate change.

Mr Cameron promised that the next Conservative government would “put rocket boosters” behind research and development projects to ensure green technology is available.

The Tory leader was particularly keen to see rapid investment in carbon capture and storage technology, which could reduce carbon emissions by power plants by an estimated 85 per cent.

Mr Cameron dismissed arguments that green policies are only affordable during times of economic upturn and said that the environment was too important to be ignored just because times were hard: “It's not that we can't afford to go green: it's that we can't afford not to go green.”

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