Sadiq Khan has called it a “wrong decision for London and Britain.”
He said ministers were “running roughshod over Londoners’ views”, and that the new runway would be “devastating for air quality across London”.
Khan said the expansion would lead to an “unacceptable level” of airport noise, as it would reach over 200,000 extra people.
His statement read: “Heathrow expansion is the wrong decision for London, and the wrong decision for the whole of Britain.
“The government are running roughshod over Londoners’ views – just five months ago I was elected as Mayor on a clear platform of opposing a new runway at Heathrow, a position that was shared by the Conservative, Liberal Democrat, Green and UKIP candidates in that election.
“A new runway at Heathrow will be devastating for air quality across London – air pollution around the airport is already above legal levels of NO2.
“Heathrow already exposes more people to aircraft noise than Paris CDG, Frankfurt, Amsterdam, Munich and Madrid combined. A third runway would mean an extra 200,000 people impacted, exposing 124 more schools and 43,200 more schoolchildren to an unacceptable level of noise.”
Mr Khan said the alternative proposal of an expanded Gatwick would “have boosted our economy without causing these huge air and noise pollution problems and it could be built quicker and cheaper”.
He added: “I will continue to challenge this decision and I am exploring how I can best be involved in any legal process over the coming months.
“Most urgently, the Government must set out how it’s possible for Londoners not to suffer from the additional air and noise pollution that we know will be created by an additional runway at Heathrow.
“They also need to guarantee that they will fully fund the billions of pounds needed to improve road and rail connections to Heathrow – Londoners cannot be expected to pick up the bill for this.”