The Airports Commission inquiry into airport expansion in the south east may be delayed for more public consultation.
The Commission’s chairman Sir Howard Davies has asked for more evidence on problems caused by air pollution.
His decision follows a Supreme Court ruling in April, ordering the UK to do more to improve air quality.
The consultation will begin immediately and end on May 29.
The three options for expansion are: a new runway at Heathrow, a new runway at Gatwick and extending one of the two existing runways at Heathrow.
The Commission was expected to make a decision on their preferred option soon after last week’s general election.