The deeper you delve into the process that is likely to result in a third runway at Heathrow, the murkier it gets. Today we reveal the extent to which BAA, the airports’ operator, colluded with the government to fix the evidence and ensure that Heathrow’s expansion would get the go-ahead. Officials at the Department for Transport were guided by BAA experts on how to strip out from their consultation document damaging data on the environmental impact of a third runway at Heathrow.

A government with a penchant for dodgy dossiers showed its colours again with the document that went into the public domain on the case for expanding capacity at Heathrow. Data on the impact of a third runway were repeatedly altered, giving the impression that its effect on noise and pollution would be negligible. Figures for carbon emissions were massaged down by the crude device of excluding incoming international flights from the calculations. BAA was effectively given a veto on the contents of the consultation document, being allowed to rewrite it.

This would be shocking enough if BAA was still a nationalised industry but it is not. BAA was privatised more than 20 years ago. It is owned, not by British shareholders, but by Ferrovial, the Spanish conglomerate. The government owes BAA nothing but it is bending over backwards to help it.

If this was not worrying enough, the Environment Agency’s as yet unpublished response to the government’s consultation document on Heathrow should be. The official watchdog on environmental issues says that when it comes to a key measure of the airport’s future impact on air quality, measured by emissions of nitrogen dioxide, the government’s evidence is not “sufficiently robust”.

The effect on air quality as a result of Heathrow’s expansion “will result in increased morbidity and mortality impacts”, in other words more illnesses and early deaths in areas unlucky enough to be under the Heathrow flightpath. Once the decision to expand the airport is made it will be too late to prevent these effects, the agency warns. As a result, it says, “there are arguments for postponing irreversible investment decisions in the face of uncertainty”.

These concerns, coming from an official environmental watchdog, blow a hole in the government’s apparent belief that it can pursue a green agenda and also preside over the irresponsible, environmentally unfriendly expansion of Heathrow. As we have argued before, it is not too late to reconsider alternative options for additional aviation capacity in the southeast, notably a new airport, suitable for the 21st century, in the Thames estuary to the east of London.

Ministers seem so beholden to BAA and Heathrow that they have closed their minds to the alternatives, whatever the cost to the environment and the quality of life. We owe it to future generations to reverse this folly.