London - A long-awaited decision on where a new runway for London should be built could be delayed to next year, media reported on Monday.
Prime Minister David Cameron had been expected to announce whether Heathrow or Gatwick would host the new runway by the end of this year.
But The Times newspaper has reported that a final decision could now be pushed back until 2016 over doubts that a new runway could meet air quality standards.
Cameron's spokesperson told reporters on Monday that there would be "a decision on plans by the end of the year".
In July, an official commission recommended that the extra runway should be built at Heathrow, one of the world's busiest international air hubs, on the western edge of London.
However many local people are opposed to the plan, which would require the demolition of homes, while environmental groups say it is incompatible with Britain's targets to limit emissions.
London Mayor Boris Johnson, a member of Cameron's Conservative party, is against the expansion of Heathrow, as is Zac Goldsmith, the Conservative candidate to replace Johnson at elections next year.
In 2009, before he became prime minister, Cameron himself made a "no ifs, no buts" promise that there would be no third runway at Heathrow.