Sadiq Khan 'ready to play active role' in legal action against Heathrow plans
Sadiq Khan has announced that he will play an "active role" in a legal challenge against a third runway at Heathrow "if required".
The London Mayor has directed Transport for London (TfL) to provide its "expert advice" to boroughs which will be affected by the airport's expansion.
Four Conservative-run local authorities - Windsor and Maidenhead, Richmond, Hillingdon and Wandsworth - together with Greenpeace have formed an alliance and instructed lawyers to prepare a case against the project.
A third runway at the west London hub would lead to hundreds of thousands more flights each year.
Mr Khan claimed that the scheme, confirmed last month as the Government's preferred plan for boosting airport capacity in south-east England, would expose an extra 200,000 Londoners to an unacceptable level of noise every day.
This included 124 schools and 43,200 schoolchildren.
He warned that aircraft noise could lead to health problems related to stress and sleep disturbance, while children could suffer from reduced reading ability and problems with memory recall.
A third runway would also add higher levels of toxic air, he added.
The councils are still considering the exact nature of their challenge. The group worked together in 2010 to win a High Court battle over plans by Gordon Brown's government to expand Heathrow.
Mr Khan said TfL was likely to be named as an interested party in the action. If that does happen the mayor will then take a decision on whether to personally join the legal challenge.
He said: "I promised I wouldn't just stand-by and see hundreds of thousands suffer from the additional noise and air pollution that a third runway would cause.
"These decisions show that I'm ready to help ensure that this misery isn't inflicted on Londoners.
"That's why I've directed TfL to provide their expert advice and assistance to support Hillingdon, Richmond, Wandsworth and Windsor and Maidenhead councils, and Greenpeace as they prepare for a joint legal challenge, and why I will be ready for us to play an active role in the action if required."
The Department for Transport (DfT) has said that Heathrow expansion will include noise and respite measures for the local area, including legally binding noise targets to encourage the use of quieter planes and a six-and-a-half hour ban on night flights.
The department also claims that the project will comply with air quality requirements and the UK's carbon obligations.