Boris Johnson has called the building of a third runway at Heathrow “barbaric” and “self-defeating”.
The London mayor said the expansion plans were “desperately short-sighted” and would be a “disaster”.
Johnson wants to build a four-runway hub airport, dubbed Boris Island, in the Thames Estuary. He claimed Gatwick would not deliver the hub capacity the UK needs, and expansion at Heathrow would create “too much noise and environmental pollution”.
The Airports Commission is expected to announce shortly whether it has shortlisted Johnson’s proposal for a new hub airport as a solution to the UK’s “capacity crisis”.
Writing in his Daily Telegraph column he described any backing for Heathrow, in west London, as "madness".
"What frustrates me is that third runway (at Heathrow) is so desperately short-sighted," he added.
“You could not conceivably get it built before 2029, by the airport's own admission - and as soon as it opened it would be full. Even with three runways, Heathrow would be lagging woefully behind our continental rivals.
“In fact, it is one of the most shameful consequences of our failure to provide more hub capacity that Amsterdam now serves more UK destinations than Heathrow itself.”
Johnson said the UK stood to lose its position as a "great trading nation" as the business lobby group the CBI demanded "spades in the ground by 2020". Its deputy director-general Katja Hall said UK businesses wants action now.
“There can be no more excuses - we need to see the Airports Commission deliver a strong case for new capacity and a clear schedule for delivery, and politicians to commit to spades in the ground by the end of the next Parliament,” she said.
"With Heathrow full and the UK slipping behind in the race for new connectivity, it is essential that the Airports Commission delivers a solution that addresses the ticking time bomb of our lack of spare hub capacity."
Last week, Heathrow CEO John Holland-Kaye urged Johnson to back its bid if the Thames estuary plan is rejected.