Noise is likely to be the key constraint against building a third runway at Heathrow, according to government documents obtained by Greenpeace.

The documents, an assessment of risks to the construction of a third runway, show that the airport may fail to meet noise limitation targets even without a new runway. The airport may also fall foul of European Union regulations on emissions of pollutants such as nitrogen dioxide.

If the levels were exceeded, the airport would face fines, unless the government is successful in obtaining an exemption.

Financial Times