Hoon: Heathrow study on pollution 'over-cautious'

The Transport Secretary has disputed a key finding of his officials in the risk register regarding the proposals to allow the west London airport to grow.

His stance will fuel the belief that Mr Hoon, Prime Minister Gordon Brown and Business Secretary Lord Mandelson will override the concerns of other Cabinet ministers to give the go-ahead for a third runway at Heathrow and greater use of the existing runways.

The register, published in October 2007, revealed that "mitigation measures identified to achieve air quality targets are too costly or impractical to implement, or politically unacceptable". It concluded that the impact of this being the case would be "high", and the likelihood of it happening as "medium".

Mr Hoon insisted in a letter to Conservative MP for Putney Justine Greening that the standard practice in compiling such documents was to describe the "combined residual risk" as high. "However, a risk register is only a snapshot at a particular point in time and should be interpreted alongside other evidence," he added.

"With hindsight, the October entry looks over-cautious."

The Transport Secretary insisted that the risks identified applied - not to a third runway - but only to changing regulations to permit take-offs and landings on both runways throughout the day, rather than alternating their use.

Local residents and environmentalists, through, believe that another runway would also add to breaches of nitrogen dioxide levels.

Ms Greening said: "A future Conservative government will cancel Heathrow expansion plans, but clearly the current Government is hellbent on expansion at whatever the costs to London communities and the environment. It is deeply irresponsible."

Meanwhile, a poll for Greenpeace found that Labour could lose at least four seats at the next general election on the back of anger over a third runway. Almost a quarter of voters in parts of west London said that they would be less likely to vote Labour if the airport was allowed to expand, though one in 10 said they would be more likely to back Mr Brown for supporting expansion.

The survey by ICM Research found a swing away from Labour of almost five per cent in six west London constituencies. Such a result would see the Government lose the seats of Battersea, Ealing Central and Acton, Hammersmith and Brentford and Isleworth, held by health minister Ann Keen, according to Greenpeace.

Ben Stewart, of the green group, said: "This polling should ring alarm bells at Labour headquarters."