New Whitehall documents show that ministers are planning to water down EU pollution curbs in order to allow Heathrow to expand.
Shadow secretary of state for transport Theresa Villiers, said: "These revelations are further worrying proof that the Government is set on building a third runway regardless of the impact it will have on the environment, quality of life and public health. They are on the wrong side of the argument on Heathrow and should scrap their plans to build a 3rd runway."
Liberal Democrat Shadow Transport Secretary, Norman Baker has written to Hilary Benn asking him to correct his apparently misleading statement. "Hilary Benn must come clean over Heathrow. It is clear that the statement I was given is at odds with the truth.
"My suspicions were always that Defra was conniving to weaken air pollution standards at Heathrow, but Hilary Benn denied it. Now we have confirmation that this was indeed what Defra was doing."
Benn had originally stated in a Parliamentary answer that plans to phase in the directive were 'not to do with any decisions that might be taken in the future about airport capacity'.
However, information received from the Department for Transport following a Freedom of information (FoI) request casts doubt on this statement. It shows that Defra and DfT officials worked together to 'ensure negotiations over the Directive take account of Heathrow position'.
"We have long given up on the Department for Transport, which is so clearly in the pocket of the aviation industry in general and BAA in particular. But the least we could have expected is that the department charged with protecting our environment - Defra - would have stood its ground," said Baker.