The Airports Commission has come out in favour of a new runway at Heathrow, throwing the issue into the political arena.
The commission's report is neutral on whether a runway should use a hybrid bill or a development consent order to get consent, but this is a key issue.
A hybrid bill would be promoted by the government and so it would have to back an option; a DCO would be promoted by the airport and so the government could remain more neutral.
The Airports Commission has backed a third Heathrow runway, saying it will add £147bn in economic growth and 70,000 jobs by 2050.The report's release has revived intense debate over the runway's environmental impact.Downing Street officials say they want to digest the report properly, without making "a snap judgement". But London's Mayor, Boris Johnson, told the BBC that a new runway would have a "catastrophic" effect.