The government is to hold a formal consultation on UK aviation – including controversial plans for a new airport in the Thames Estuary.
The study, to begin in March, will look at options for “‘maintaining the UK’s aviation hub status'”.
David Cameron has ruled out expanding Heathrow but his deputy Nick Clegg is said to be opposed to the estuary idea.
The airport would be built partly on reclaimed land and could be on either an island or a peninsula. But concerns have been raised about damage to the environment.