A third runway at Heathrow would be "unlawful", its rival Gatwick claimed today.
It says expansion at Heathrow would breach strict European air quality limits. Gatwick, meanwhile, claims it would meet all limits with a second runway and expansion should be in Sussex.
But Heathrow has hit back saying it would put measures in place to mitigate and the airport is the best place for expansion with tens of thousands of new jobs boosting the local economy.
The row erupted on the final day of consultation on pollution by the Airport Commission, which will make a recommendation on a new runway at Heathrow or Gatwick in the next few weeks.