The government is said to want more evidence on environmental issues before making a decision on the location of an extra airport runway in London.

Critics, however, say the six month delay – pushing the verdict back to June – is a cynical ploy to avoid an embarrassing row over Heathrow during the London mayor election in May.

Current mayor Boris Johnson is opposed to Heathrow expansion, as is the Tory candidate Zac Goldsmith. His Labour rival Sadiq Khan, who also opposes a third runway at Heathrow, said: “We won’t forgive David Cameron if this is just a postponement to spare his mayoral candidate Zac Goldsmith’s embarrassment during the campaign.”

David Cameron gave a “guarantee” in July that a final decision would be made by the end of the year.

That followed the publication of the independent report of the Davies Commission, which recommended a third runway at Heathrow rather than the expansion of Gatwick Airport.

Senior ministers are meeting on Thursday to discuss the matter and No 10 tonight refused to confirm that will now happen.

The Prime Minister’s spokeswoman said: “We will respond to the Davies report by the end of the year.”