Hilary Benn, the environment secretary, lifted the lid yesterday on the Cabinet-level debate on the expansion of Heathrow, saying the government must not contemplate allowing itself to breach air pollution limits set by the European commission.

His intervention could potentially put a break on government expansion plans. Air pollution around Heathrow already exceeds limits set by the commission and Britain is expected to seek a temporary abrogation from an air pollution directive agreed in June, but only on the basis that it will be able to meet the pollution requirements by 2015, the deadline set by the commission.

Britain will have to satisfy the commission that Heathrow's expansion will not undermine Britain's ability to meet its commitments by 2015. Much of the pollution around Heathrow is caused by heavy traffic on the nearby motorway, and critics of the expansion claim it defies logic to suggest that the airport will be able to meet the commission requirements by 2015, since a third runway is planned that would increase air traffic, passenger numbers and vehicle journeys to the airport.

In an interview in the Sunday Times, Benn does not disagree with the government's consultation process, or directly say it is unrealistic to expect Britain to meet the commission's pollution requirements by 2015 if expansion is agreed. But he underlines the implications of ignoring the commission's directive, saying: "You are then in trouble with the commission, you get infraction proceedings and then off you go - which is not something we can contemplate." Benn's advisers confirmed the accuracy of the quotations, which were made in an interview primarily designed to discuss food policy. His department is responsible for noise and air quality, two of the three key issues the government has said it will take into account before giving the third runway the go-ahead.

The third environmental consideration is the impact on road traffic. Earlier this month, the transport secretary, Geoff Hoon, announced a delay until January on whether to give the scheme the go-ahead, partly as a result of cabinet divisions. Advocates of Heathrow expansion claim a new generation of aircraft will be less polluting and less noisy than their predecessors. But opposition politicians claim on the basis of freedom of information requests that BAA, the airport operator, tried to fix the figures on pollution projections.

In a Commons debate last month Hoon told MPs: "The problems are mainly to do with existing pollution from traffic in Greater London, including around Heathrow, and traffic in other major cities across the country. They are not to do with decisions about future capacity at Heathrow. "Reports that we are seeking to abrogate from our responsibilities in this area solely in order to promote expansion at Heathrow are completely and utterly wrong."


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