Heathrow chiefs are confident the airport can meet Government environmental targets and will be granted permission to expand after it was announced the decision will be delayed until summer 2016.

The Government said more research into the environmental impact of expansion was needed and the decision, previously expected to be made by the end of this year, will not come until at least six months from now.

The delay has been lambasted with Labour accusing the Government of politicising the decision in a bid to boost its Mayoral campaign ahead of the May election.

Transport secretary Patrick McLoughlin said: "The case for aviation expansion is clear - but it's vitally important we get the decision right so that it will benefit generations to come.

"We will undertake more work on environmental impacts, including air quality, noise and carbon."

Heathrow’s environment and sustainability director, Matt Gorman, said he is fully confident the airport can meet Government targets and he expects Heathrow will become the world's "most environmentally responsible hub."

He said: "Importantly it is not just us that has been saying that. The Airports Commission spent three years and £20m reaching the same conclusions that we can meet environmental targets."

Mr Gorman refused to speculate on whether the delay is part of Conservative political strategy given Zac Goldsmith’s pledge to stand down from his Richmond Park seat and his mayoral ambitions.

Labour MP and Mayoral candidate Sadiq Khan accused the Government of "kicking the decision into the long grass" to avoid embarrassing the Conservative Mayoral candidate.

Mr Goldsmith denied having conversations with ministers about delaying the decision in order to protect his campaign for London mayor.

Speaking at a canvassing event in Purley on Thursday, Mr Goldsmith said: "I've not been given any indication of what the Government is going to be doing.

"You don't know what the Government is going to say and nor do I. I'm studiously avoiding speculation."

Mr Gorman refused to speculate on any link between the Mayoral campaign and the delay but said: "We have always recognised that there’s some local opposition to expansion and we are committed to working with local groups and Mr Goldsmith but it is in the national interest to expand."

Mr Khan, who is backing Gatwick airport for expansion, said: "We can’t afford more dithering over aviation capacity."

The Tooting MP added: "We already know Heathrow can’t be the solution.

"The additional damage from air and noise pollution would mean more years of delay, while protracted legal battles are fought.

"It must be Gatwick - and we need to get on with it."