GATWICK may have been thrown a lifeline in the battle for a new runway after the Transport Secretary insisted air quality would be a “major consideration” in deciding were to expand.

Patrick McLoughlin said the issue was being taken "incredibly importantly" by ministers surrounding the Government’s decision on airport expansion.

Building a third runway at Heathrow was recommended in July by the Airports Commission, which rejected expansion of Gatwick.

But Heathrow currently breaches air quality limits while Gatwick is within the legal limit.

Gatwick chief executive Stewart Wingate said: "Heathrow's poor air quality already breaches legal limits and it is difficult to see how expansion could legally go ahead with the millions of extra car journeys an expanded Heathrow would generate.

"In stark contrast, Gatwick is well within legal air quality limits and can guarantee we would remain so with a second runway."

Sir Howard Davies, chairman of the Airports Commission, wrote to the Transport Secretary last month to state that "appropriate measures" can be taken to address air quality at an expanded Heathrow and claimed "limited weight" should be placed on the suggestion that the issue "represents a significant obstacle".

Mr McLoughlin said: "We take climate and we take air quality incredibly importantly, so it will be a major consideration in the decisions we make."

Heathrow has committed to having no more airport related road traffic after expansion by improving rail links to encourage passengers and staff to use public transport.

It also wants the London low emission zone to be extended to the airport area and local diesel buses to be replaced with cleaner vehicles.

A Heathrow spokesman said: "The Government's Airports Commission confirmed a third runway at Heathrow can go ahead without breaching air quality legal limits, as long as we continue to implement our mitigation plans."

Mr McLoughlin said ministers were also examining the work done by manufacturers to reduce aircraft emissions and would take into account the impact of expansion on the country's economy.

"We have got to look at what do companies like Rolls-Royce - who are at the leading edge of improving the emissions from aircraft - are doing, and make sure that the United Kingdom overall is not put at an economic disadvantage," he added.

Prime Minister David Cameron is due to announce a decision on expansion by the end of the year.