THE airports operator BAA colluded with government officials to “fix” the evidence in favour of a new third runway at Heathrow, an investigation has found.

Documents seen by The Sunday Times reveal that BAA executives prevented the use of data in the consultation document which showed that the expansion would cause unlawful levels of pollution and extra noise.

Instead, they gave civil servants amended data that showed the anticipated 230,000 extra flights a year at Heathrow would have a minimal impact on noise and pollution levels.

A leaked report shows the government’s own watchdog, the Environment Agency, has now criticised the Department for Transport (DfT) consultation document into the third runway as flawed and incomplete.

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The agency says the science is not “sufficiently robust” to sustain the document’s backing for a third runway and that it has neglected to consider the health impact of the extra pollution, which could increase the risk of serious illness and deaths in the area.

One official who was involved in “Project Heathrow” – the DfT unit that researched the environmental impact of the runway - said: “It’s a classic case of reverse engineering. They knew exactly what results they wanted and fixed the inputs to get there. It’s appalling.”

Previously unpublished documents obtained under freedom of information laws show: BAA gave instructions to DfT officials on how to “strip out” data that indicated key environmental targets would be breached by the airport. The airports operator repeatedly selected alternative data used for the consultation to ensure that the final results showed a negligible impact on noise and pollution. The DfT gave BAA unprecedented access to confidential papers and allowed the company to help to rewrite the consultation document. The final document significantly reduced the likely carbon emissions caused by the runway by not including incoming international flights.

BAA, Britain’s biggest airports operator, owns seven of the country’s airports including Gatwick and Stansted as well as Heathrow.

The company says a third runway is vital to maintain Heathrow’s position in world aviation. Critics say that it is a cynical attempt by BAA to sustain its profits and its grip on the market, irrespective of the impact on the environment and residents.

The consultation on the third runway closed last month but organisations opposing the expansion plan, including local councils, are likely to launch a legal challenge if it is given the go-ahead. Justine Greening, a shadow Treasury minister and MP for Putney, southwest London, said: “It would be a disastrous decision to build a third runway, but [the document] has been fixed in the most reckless way. It’s indefensible.”

Edward Lister, leader of Wandsworth council, south London, said: “There should be an independent investigation of what looks like collusion between the government and a private company. It makes a sham of the consultation. Any decision on a third runway must be put on hold.”

The case against the consultation document is likely to be strengthened by the official response of the Environment Agency, leaked last week to The Sunday Times. The agency criticises the lack of work on the impact on air quality, describing it as potentially “a very significant omission”, adding that there are “substantive uncertainties” over whether an expanded Heathrow could meet European Union pollution limits.

It also warns that the document fails to consider the impact on public health of pollution from emissions such as nitrogen dioxide and particulates. There was the potential for “increased morbidity and mortality over a dense local population”, it says.

The agency’s response concludes that the case is “not made” that the third runway would meet air quality targets and suggests there was an argument for postponing the project.

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