Gatwick says 66% of councillors in London support its expansion against 44% for Heathrow.
And half of the 203 councillors asked said the certainty a runway scheme can be delivered has become more important since Brexit.
The result of the YouGov poll for the West Sussex airport came after a cross party group of 11 London councils urged prime minister Theresa May to support a new runway at Gatwick and abandon proposals to expand Heathrow.
The Leaders of Croydon, Hammersmith & Fulham, Hillingdon, Kensington & Chelsea, Kingston, Lambeth, Lewisham, Merton, Richmond, Southwark and Wandsworth councils highlighted the “broad and growing consensus behind Gatwick expansion” and pledged to work with ministers to support this “bold and ambitious project.”
The authorities represent around 2.8million Londoners and include five Conservative and six Labour controlled boroughs.
In a letter to May, they said: “We now know that Gatwick expansion offers a similar economic stimulus to Heathrow but with no cost to the public purse and a fraction of the environmental upheaval.
“It does not face the same legal obstacles and would create a more balanced, resilient and competitive airports network rather than putting all of our eggs in the Heathrow basket.”
Gatwick CEO Stewart Wingate said: “London has united behind Gatwick expansion as the only scheme that gives us guaranteed growth while limiting the impact on the environment.
“Crucially Gatwick expansion is the only plan that can actually be delivered and – unlike Heathrow – it does not need £5 billion of taxpayer funding.
“This money could otherwise be put towards vital infrastructure projects such as Crossrail 2, Thames river crossings and new homes.
“The UK cannot afford decades more of Heathrow delay – let’s get on and build a new runway at Gatwick.”