UPDATE 1-Britain due to decide on new London runway amid political chaos

(Adds Heathrow details)

By Sarah Young

LONDON, June 27 (Reuters) - Britain is set to fall down theEuropean league table for hub airports, the boss of Heathrowsaid on Tuesday, as he urged the government to back a thirdrunway to protect trade links and send the message that Britainremains open for business.

The British government said on Monday it would announce inweeks whether it backed the expansion of Heathrow or Gatwick,but fears are growing that the long-awaited investment decisioncould become a victim of the political chaos that has beenthrown up by the vote to leave the European Union.

"Now more than ever, Britain needs to underpin its globallyrecognised economic strength by delivering privately fundedinfrastructure projects like a third runway," Heathrow CEO JohnHolland-Kaye told a London conference.

"The future economic security of this country depends onBritain being an outward-looking trading nation."

Prime Minister David Cameron's government has taken fouryears to decide where to build a new runway, with Heathrow seenas the front-runner over rival Gatwick.

But Cameron is now set to resign by October, and the formerLondon mayor Boris Johnson, the favourite to succeed him, hasopposed expansion at Heathrow and once said he would lie down infront of the bulldozers to stop a third runway being builtthere.

Heathrow, located close to densely populated west London, isthe largest hub airport in Europe and Britain's busiest, butHolland-Kaye cited research showing that it would soon beovertaken by France by around 2020.

It will then fall behind Istanbul, Frankfurt and Amsterdamin terms of the busiest hub.

Past attempts to expand Heathrow have been hampered by localopposition, due to worries about increased noise and airpollution.

The chief executive of Gatwick, located south of the city ina less populated area, is due to say in a speech to the sameconference that Brexit has strengthened his argument that itwould be easier and more effective to build the runway there.

"It is now clearer than ever that only Gatwick can deliverthe new runway Britain needs," Gatwick Chief Executive StewartWingate will say on Tuesday, according to extracts of the speechprovided by the airport to media.

"In these uncertain times that means Gatwick can give thecountry certainty of delivery. Britain cannot afford yet moredelay."

On Monday, 50 business leaders including the CEOs of brokerICAP, real estate company Land Securities andinsurer Legal & General published a letter in the Timessaying the Brexit vote made the need for a new runway morepressing given that Britain would need to increase trade witheconomies beyond the EU. (Editing by Kate Holton and Stephen Addison)