Heathrow's controversial third runway – due to be given the green light by ministers this week – is unlikely ever to be built because it will fall foul of new European pollution laws, environmentalists and senior government advisers believe.

The airport's two existing runways already cause air pollution which breaches compulsory European Union air-quality standards, which Britain will have to observe by 2015. Neither anti-runway campaigners nor the Government's Environment Agency see how these can possibly be met if the number of flights rises by 50 per cent as planned.

The Conservative and Liberal Democrat parties have vowed to block the new runway if they are in a position to do so after the next election. They plan to force a parliamentary vote on the project, which would be almost certain to attract Labour rebels.

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The go-ahead – pencilled in for confirmation by Geoff Hoon, the Secretary of State for Transport, on Thursday – is to be presented as the centrepiece of a New Deal-style series of public works, like the one president-elect Barack Obama is expected to push through in the US after taking office later this month.

In an attempt to reduce the impact of one of the most hotly contested planning decisions for years, the move will be accompanied by a list of multibillion-pound projects designed to demonstrate the Government's commitment to improving transport and other facilities across the nation. It will be linked to the establishment of "an international rail hub" at the airport, the Crossrail project, preparations for the London Olympics and plans to accelerate the Government's school-building programme.

Ministers will also insist that the plans for the runway will have to ensure that the air around Heathrow – already polluted by road traffic as well as by existing flights – does not breach EU limits for nitrogen dioxide, due to come into force next year. Britain can apply for a five-year delay but will have to observe them by 2015.

The British Airports Authority says that new technology and cleaner planes will reduce pollution as to enable the standards to be met, but critics do not see how this can be done if flights rise to more than 700,000 a year, when the existing 480,000 already help to put parts of the area over the limit.

Lord Smith, the chairman of the Environment Agency, said yesterday that the runway could not go ahead unless "very strict pollution limits" were set. He was sceptical that the EU standards could be met, and would prefer that the runway was not built.

John Stewart, the chairman of Hacan Clearskies, which leads opposition to the project, said yesterday: "The runway will never see the light of day."