Sir Howard Davies has decided to launch a new public consultation into the expansion of either Heathrow or Gatwick airports in a bid to avert a potential legal challenge to the three-year review.
The Three Options for Expanding London's Airports:
A new runway at Heathrow
Extending one of the two existing runways at Heathrow
A new runway at Gatwick
The review was due to present its findings soon after the 7 May elections. The move comes after the Supreme Court ruled in April that the UK must speed up its efforts to tackle air pollution after continuously breaching EU limits.
The commission has already recommended three options for a new runway, and the consultation will begin immediately and end on Friday 29 May.
The final report was expected next month, but could now be delayed as a result of the consultation, raising fears that Sir Howard will not be able to devote much time to it as he is taking up his new post of chairman of the Royal Bank of Scotland.
Business leaders and the airline industry have repeatedly warned against further delays to a decision postponed several times by successive governments. Heathrow is already at full capacity, and a new runway is seen as vital to UK growth and trade.
Heathrow's bid for expansion has been criticised by local residents and environmentalists because that the roads surrounding the airport already breach EU air pollution limits.
A previous government decision to allow a third runway at Heathrow was overturned by the courts in 2010 on environmental grounds, and Gatwick has always claimed that expansion at Heathrow could again be challenged legally.
The commission's decision to seek further public comment will be an extra safeguard against any judicial review. "It could be vulnerable unless they do something," one person close to the bidders told the Financial Times.